<PAGE>
 
                      SECURITIES AND EXCHANGE COMMISSION

                            Washington, D.C.  20549

                                   FORM S-8

                         REGISTRATION STATEMENT UNDER
                          THE SECURITIES ACT OF 1933


                             PITT-DES MOINES, INC.
            (Exact name of registrant as specified in its charter)


Commonwealth of Pennsylvania                                      25-0729430
(State or other jurisdiction of                                 (IRS Employer
incorporation or organization)                               Identification No.)


10200 Grogan's Mill Road,  The Woodlands, Texas                      77380
   (Address of Principal Executive Offices)                        (Zip Code)

                             PITT-DES MOINES, INC.
                    LONG TERM INCENTIVE STOCK PLAN OF 1997
                           (Full title of the plan)

               R. A. Byers, Vice President Finance and Treasurer
                             Pitt-Des Moines, Inc.
                      10200 Grogan's Mill Road, Suite 300
                          The Woodlands, Texas  77380
                    (Name and address of agent for service)

                                (281) 774-2200
         (Telephone number, including area code, of agent for service)


                        CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
============================================================================================================================
                                                        Proposed                   Proposed
      Title of                    Amount to             maximum                     maximum                   Amount of
   securities to be                   be             offering price                aggregate                 registration
     registered                   registered           per share                 offering price                  fee
---------------------------     ---------------     ----------------          ---------------------        -----------------
<S>                               <C>                 <C>                       <C>                          <C>
   Common Stock                   706,000             $17.56(1)                 $12,397,360 (1)               $3,446.47
    (no par value)                 shares
   Common Stock                   694,000             $23.25(2)                 $16,135,500 (2)               $4,485.67
    (no par value)                 shares
      TOTALS                    1,400,000                 -                              -                    $7,932.14
                                   shares
============================================================================================================================
</TABLE>
(1)  Estimated solely for purposes of calculating the registration fee pursuant
     to Rule 457(h).  The price is the exercise price of the stock options
     granted to date.

(2)  Estimated solely for purposes of calculating the registration fee pursuant
     to Rule 457(h). The price has been determined in accordance with
     Rule 457(c) which is the average of the high and low prices of the Common
     Stock on the American Stock Exchange on December 11, 1998.
<PAGE>
 
PROSPECTUS
----------


                             PITT-DES MOINES, INC.

                    LONG TERM INCENTIVE STOCK PLAN OF 1997

                       1,400,000 SHARES OF COMMON STOCK


     This Prospectus relates to up to 1,400,000 shares of our common stock, no
par value (the "Common Stock") which are being offered pursuant to the Pitt-Des
Moines, Inc. Long Term Incentive Stock Plan of 1997 (the "Plan") described
herein.

     You may receive shares of our Common Stock under the Plan from a restricted
stock grant or stock option grant made to you.

     This Prospectus cannot be used to reoffer or resale the Common Stock you
may acquire under the Plan.

     Our Common Stock is traded on the American Stock Exchange.

     If you do not already have our latest Annual Report, we will provide it
with the Prospectus.

     Neither the Securities and Exchange Commission nor any other state
securities commission has approved or disapproved of these securities or passed
upon the accuracy or adequacy of this prospectus.  Any representation to the
contrary is a criminal offense.


--------------------------------------------------------------------------------


                             PITT-DES MOINES, INC.

                      10200 GROGAN'S MILL ROAD, SUITE 300
                           THE WOODLANDS, TX  77380
                                 281-774-2200

               THE DATE OF THIS PROSPECTUS IS DECEMBER 11, 1998.

                THIS DOCUMENT CONSTITUTES PART OF A PROSPECTUS
                 COVERING SECURITIES THAT HAVE BEEN REGISTERED
                       UNDER THE SECURITIES ACT OF 1933.
<PAGE>
 
                                   CONTENTS

                                                                       Page
                                                                       ----

Availability of Additional Information About the Company................iii
General Information.....................................................  1
Description of the Plan.................................................  2
     1.  Administration.................................................  2
     2.  Eligibility and Participation..................................  2
     3.  Shares Available for Issuance..................................  3
     4.  Types of Grants................................................  3
     5.  Option Price...................................................  3
     6.  Option Period, Exercise........................................  4
     7.  Restricted Stock...............................................  5
     8.  No Right to Employment.........................................  5
     9.  Tax Withholding................................................  6
    10.  Payment........................................................  6
    11.  Options Not Transferable.......................................  6
    12.  Surrender of Options, Return of Shares.........................  7
    13.  Adjustment in Number, Price of Shares..........................  7
    14.  Amendment, Discontinuance, Term, Assignment....................  8
Certain Federal Income Tax Consequences.................................  8
Restrictions on Reoffers and Resales.................................... 10
Incorporation of Certain Documents by Reference......................... 10
Stockholder Reports and Current Supplements to Prospectus............... 11
Experts................................................................. 12
Legal Matters........................................................... 12


                                      ii
<PAGE>
 
           AVAILABILITY OF ADDITIONAL INFORMATION ABOUT THE COMPANY

     We are subject to the Securities and Exchange Act of 1934, as amended (the
"Exchange Act"), and file reports, proxy statements and other information with
the Securities and Exchange Commission (the "Commission").

     Those documents can be inspected and copied at the Public Reference Section
of the Commission at Judiciary Plaza, 450 Fifth Street, N.W., Washington, D.C.
20549; and at the Commission's regional offices at Northwestern Atrium Center,
500 West Madison Street, Suite 1400, Chicago, Illinois 60661-2511; and Seven
World Trade Center, 13th Floor, New York, New York 10048.  Copies of this
material can also be obtained at prescribed rates from the Public Reference
Section of the Commission at Judiciary Plaza, 450 Fifth Street, N.W.,
Washington, D.C. 20549.  Reports, proxy statements and other information
concerning the Company may also be inspected at the offices of the American
Stock Exchange.

     We have filed with the Commission a Registration Statement on Form S-8
(herein, together with all amendments and exhibits thereto, referred to as the
"Registration Statement") under the Securities Act of 1933, as amended (the
"Securities Act"), for our Common Stock and the Plan.  This Prospectus does not
contain all of the information in the Registration Statement and its exhibits;
certain parts have been omitted in accordance with the Commission's rules and
regulations. You may refer to the Registration Statement for further
information.  The Registration Statement, including exhibits, may be inspected
without charge and copied at the Public Reference Section of the Commission at
450 Fifth Street, N.W., Washington, D.C. 20549, and at the regional offices of
the Commission described above.  Electronic registration


                                      iii
<PAGE>
 
statements made through the Electronic Data Gathering Analysis and Retrieval
(EDGAR) system are publicly available through the Commission's web site 
(http://www.sec.gov).

     We will provide you free, upon request, a copy of any information
incorporated by reference in Item 3 of Part II of the Registration Statement.
These documents are incorporated herein by reference.  Requests for copies and
additional information about the Plan and its administrator should be directed
to Pitt-Des Moines, Inc., 10200 Grogan's Mill Road, Suite 300, The Woodlands,
Texas 77380, Attention: R. A. Byers, Vice President, Finance and Treasurer,
(281) 774-2200.  We will also provide you free, upon request, a copy of any
documents required to be delivered to you by Rule 428(b) under the Securities
Act.


--------------------------------------------------------------------------------

     You should rely only on the information contained in this document or
others that we have referred you to.  We have not authorized anyone to provide
you with information that is different from that contained in this Prospectus.
The information contained in this Prospectus is accurate only as of the date of
the information contained in this Prospectus, regardless of the time of delivery
of this Prospectus or of any sale of the Common Stock.


                                      iv
<PAGE>
 
                             PITT-DES MOINES, INC.

                    LONG TERM INCENTIVE STOCK PLAN OF 1997
                              
                              GENERAL INFORMATION

     Pitt-Des Moines, Inc. (the "Company"), 10200 Grogan's Mill Road, The
Woodlands, Texas 77380, (281-774-2200), is the sponsoring employer and issuer of
shares of common stock, no par value (the "Common Stock") that may be granted to
or purchased by eligible employees of the Company and its Subsidiaries under the
Pitt-Des Moines, Inc. Long Term Incentive Stock Plan of 1997 (the "Plan").  The
Plan was adopted by the Board of Directors of the Company on November 6, 1997,
subject to approval by the stockholders of the Company which was obtained on
May 7, 1998. The number of shares of the Company's Common Stock that may be
granted or purchased under the Plan is 1,400,000 shares. All shares or options
granted under the Plan must be granted not later than November 1, 2007.

     The purpose of the Plan is to promote the long-term growth and
profitability of the Company by providing certain officers and key employees of
the Company and its Subsidiaries with incentives to maximize stockholder value,
otherwise contribute to the success of the Company and enable the Company to
attract, retain and reward the best available persons for positions of
substantial responsibility, all as determined by the Committee in its
administration of the Plan.  The Plan is not subject to the provisions of the
Employee Retirement Income Security Act of 1974.

                                       1
<PAGE>
 
                            DESCRIPTION OF THE PLAN

     The following description is intended to summarize provisions of the Plan.
It is not a complete statement of the Plan or its operation and is qualified in
its entirety by reference to the complete text of the Plan.  Prospective
participants should become familiar with the text of the Plan.  A current copy
of the Plan is on file with the Secretary of the Company and may be reviewed by
participants or prospective participants in the Plan upon request.  Unless
defined in this Prospectus, each capitalized term used below is defined and has
the meaning ascribed to it in the Plan.

1.   ADMINISTRATION

     The Plan will be administered by a committee (the "Committee") consisting
of at least three directors of the Company who will be appointed by and serve at
the pleasure of the Board of Directors.  Subject to the terms of the Plan, the
Committee will select from eligible employees those persons to whom options and
restricted stock will be granted, the number of shares to be included in each
grant or option, the option price and the period during which each option may be
exercised and during which each grant and/or option may vest.

2.   ELIGIBILITY

     Options and shares of restricted stock may be granted under the Plan to
officers and key employees of the Company and its Subsidiaries (including
officers and employees who are directors of the Company) who, in the opinion of
the Committee, are mainly responsible for the continued growth, development and
future financial success of the business of the Company. As

                                       2
<PAGE>
 
of the date of this Prospectus, there are approximately 9 officers and key
employees of the Company and its Subsidiaries who may be eligible generally to
participate under the Plan.

3.   SHARES AVAILABLE FOR ISSUANCE

     The total number of shares which may be issued pursuant to the Plan is
1,400,000 shares of the Common Stock of the Company.  The shares may be either
authorized and unissued shares or shares held in the treasury of the Company.
This number of shares is subject to adjustment to prevent dilution or
enlargement of rights under the Plan.  Shares covered by options or restricted
stock granted under the Plan that terminate or expire without being exercised
will remain available for the granting of future shares of restricted stock or
options under the Plan.  All shares of restricted stock or options granted under
the Plan must be granted before November 1, 2007.

4.   TYPES OF GRANTS

     The Plan provides for the Committee, in its discretion, to grant only
shares of restricted stock or options which are Non-Qualified Stock Options
under the Internal Revenue Code.  See "Certain Federal Income Tax Consequences"
below for a summary of the differing tax consequences for Non-Qualified Stock
Options and grants of restricted stock.

5.   OPTION PRICE

     The price at which each share covered by an option granted under the Plan
may be purchased will be determined in each case by the Committee but shall not
be less than the fair

                                       3
<PAGE>
 
market value of the share at the time the option is granted. Fair market value
is defined in the Plan to be the average of the high and low sales prices per
share for the Common Stock of the Company as reported on the stock exchange on
which the stock is traded on the date immediately preceding the relevant date
under the Plan or, if no sales were made on that date, on the closest preceding
date on which there were sales reports. On December 11, 1998, such fair market
value for the Company's Common Stock was $23.25 per share.

6.   OPTION PERIOD AND EXERCISE OF OPTIONS

     An option may be exercised in whole at any time or in part from time to
time within such period as may be determined by the Committee provided that the
option period may not exceed ten (10) years from the granting of the option. If
the optionee ceases to be employed by the Company or any of its subsidiaries for
any reason other than death, disability, Deferred Retirement (retirement past
age 65), Normal Retirement (retirement at age 65) or Early Retirement
(retirement before age 65), the option may be exercised only within 90 days
after termination of optionee's employment (unless termination is for Cause in
which case the option expires immediately upon termination). A termination for
Cause is when employment is terminated for committing a crime, disloyalty,
grossly negligence performance or the like. In the event of optionee's death,
disability or Early Retirement, the option may be exercised within 1 year after
the date of death, disability or Early Retirement. Should optionee take Deferred
Retirement or Normal Retirement, the option may be exercised within 3 years from
the date of optionee's Deferred Retirement or Normal Retirement.

                                       4
<PAGE>
 
7.   RESTRICTED STOCK

     Grants of restricted stock may be made by the Committee from time to time
pursuant to the Plan, such grants being subject to such restrictions as the
Committee deems appropriate, provided that in no event shall any grants of
restricted stock vest more than ten years after the date of grant.  Except as
otherwise provided by the Committee, from and after the date of grant, during
periods of restriction or otherwise, shares granted as restricted stock shall
have all of the rights of a holder of Common Stock, including but not limited to
the rights to vote and receive dividends.

8.   NO RIGHT TO CONTINUED EMPLOYMENT

     In consideration for each grant of an option or restricted stock, the
optionee (or grantee as the case may be) shall agree to remain in the employment
of the Company or a Subsidiary for at least one (1) year from the date of the
grant.  Nothing contained in the Plan nor in any stock option agreement or
agreement concerning restricted stock shall confer upon any grantee or optionee
any right with respect to the continuance of employment by the Company or any of
its Subsidiaries nor interfere in any way with the right of the Company or any
Subsidiary to terminate his or her employment or change his or her compensation
at any time.

                                       5
<PAGE>
 
9.   TAX WITHHOLDING

     Prior to the delivery of certificates for shares to be issued under the
Plan the Company has the right to require the grantee or optionee to remit to
the Company an amount sufficient to satisfy required income tax withholding.

10.  PAYMENT

     The price of each share purchased pursuant to an option shall be paid in
full at the time of each exercise of the option by any combination of the
following:  (i) in cash; (ii) by delivery of Common Stock with a Fair Market
Value equal to the Exercise Price; (iii) by delivery of irrevocable instructions
of sale to a broker on terms satisfactory to the Company to pay the Exercise
Price; or (iv) by authorizing the Company to withhold Common Stock with a Fair
Market Value equal to the Exercise Price.  Participants will not be required to
pay the Company consideration for grants of restricted stock.

11.  OPTIONS NOT TRANSFERABLE

     Options are not transferable by the optionee except by qualified domestic
relation's order or by will or the laws of descent and distribution.  During the
lifetime of the optionee, options may be exercised only by the optionee or by
his or her guardian or legal representative.

                                       6
<PAGE>
 
12.  SURRENDER OF OPTIONS, RETURN OF RESTRICTED SHARES

     The Committee, in its sole discretion, may permit an optionee voluntarily
to surrender for cancellation an option granted under the Plan, such surrender
to be conditioned upon the granting to such optionee of a new option under the
Plan for the same or a different number of shares as the option surrendered, or
may require such voluntary surrender as a condition precedent to the grant of a
new option to such optionee.  Any such new option shall be exercisable at the
price, during the period, and in accordance with any other terms and conditions
specified by the Committee at the time the new option is granted, all determined
in accordance with the provisions of the Plan without regard to the price,
period of exercise, or any other terms or conditions of the option surrendered
for cancellation.  Shares covered by options granted under the Plan and
subsequently surrendered for cancellation would again be available for the
granting of options or as grants of restricted stock under the Plan.  In the
event that the conditions for vesting of any option or restricted shares shall
fail to occur, any shares subject to such unvested option or restricted shares
returned by reason of the failure to vest, would again be available for the
granting of options or as grants of restricted stock under the Plan.

13.  ADJUSTMENT OF NUMBER AND PRICE OF SHARES

     The Plan contains provisions with respect to the adjustment of the number,
kind and price of shares covered by options or restricted stock agreements, and
the number of shares subject to the Plan which are not covered by restricted
stock agreements or options as the result of stock dividends, reorganization,
recapitalization, stock split-up, combination of shares, merger or consolidation
and other corporate changes.

                                       7
<PAGE>
 
14.  AMENDMENT OR DISCONTINUANCE

     The Board of Directors may alter, amend, suspend or discontinue the Plan,
provided that no such action shall deprive any person, without such person's
consent, of any rights previously granted pursuant to the Plan.


                    CERTAIN FEDERAL INCOME TAX CONSEQUENCES

     Under existing federal income tax laws, an employee who receives a stock
option or shares of restricted stock under the Plan which are subject to
restrictions which create a Substantial Risk of Forfeiture (as defined under
Section 83 of the Internal Revenue Code) will not normally realize any income
with respect to the stock option or restricted stock, nor will the Company be
allowed to take a corresponding deduction for federal income tax purposes, in
the year of the grant or award.

     When a non-qualified stock option granted pursuant to the Plan is
exercised, the option-holder will realize ordinary income measured by the
difference between the aggregate exercise price of the shares of Common Stock
underlying the option which is exercised, and the aggregate fair market value of
such shares of Common Stock on the exercise date. The Company will be entitled
to take a federal income tax deduction equal to the amount the employee is
required to treat as ordinary income.

     An employee who receives restricted stock subject to restrictions which
create a Substantial Risk of Forfeiture will normally realize taxable income on
the date the shares of restricted stock become transferable or are no longer
subject to Substantial Risk of Forfeiture. The amount of such taxable income
will be equal to the amount by which the fair market value

                                       8
<PAGE>
 
of the shares of Common Stock on the date such restrictions lapse (or any
earlier date on which the shares become transferable) exceeds their purchase
price, if any. An employee may elect within thirty (30) days of any grant,
however, to include in income in the year of grant the excess of the fair market
value of the shares of Common Stock (without regard to any restrictions) on the
date of grant over their purchase price, if any.

     Any income from the restricted stock, i.e., dividends, received by the
employee constitutes additional compensation and will be included in the
employee's gross income for the year when the income is received, subject to
withholding.  If any employee makes the above election to include in the year of
grant the excess of the fair market value of shares of Common Stock over their
purchase price, then any income from the restricted shares during the period of
restrictions would be dividend income and not additional compensation.

     Upon accelerated exercisability of options and accelerated lapsing of
restrictions on restricted stock in connection with a change in control of the
Company, certain amounts associated with such awards could, depending upon the
individual circumstances of the participant, constitute "excess parachute
payments" under the golden parachute provisions of the Internal Revenue Code.
Pursuant to these provisions a participant will be subject to a 20% excise tax
on any excess parachute payment and the Company will be denied any deduction
with respect to such excess parachute payment.  The limit on the Company's
deductibility of compensation under Section 162(m) of the Internal Revenue Code
is also reduced by the amount of any excess parachute payments.  Whether amounts
constitute excess parachute payments depends upon, among other things, the value
of the awards accelerated and the past compensation of the participant.

                                       9
<PAGE>
 
                     RESTRICTIONS ON REOFFERS AND RESALES

     This Prospectus will not be available for reoffers or resales of Common
Stock acquired by "affiliates" of the Company or any Subsidiary under the Plan.
Directors, officers and control persons of the Company may be considered
"affiliates" of the Company and, as such, may transfer shares of Common Stock,
including shares purchased through the Plan, only in compliance with the
registration requirements of the Securities Act of 1933, as amended (the "Act"),
or in compliance with an exemption therefrom. Generally, in the absence of
registration under the Act, shares of Common Stock held by such persons may be
sold pursuant to an available exemption from the registration requirement of the
Act such as Rule 144 of the Commission. Grantees and optionees who may be
"affiliates" are urged to consult legal counsel prior to any proposed sale of
Common Stock. Consistent with the provisions of the Act, the Company may place a
restrictive legend on Common Stock issued to such persons and issue stop order
instructions to the Company's transfer agent.


                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

     The following documents filed with the Securities and Exchange Commission
are incorporated by reference in this Prospectus:

     1.   The Company's latest Annual Report on Form 10-K filed pursuant to
Section 13 or 15(d) of the Securities Exchange Act of 1934 ("Exchange Act");

     2.   All other reports filed pursuant to Section 13(a) or 15(d) of the
Exchange Act, as amended, since December 31, 1997; and

                                       10
<PAGE>
 
     3.   The description of the Common Stock contained in the Company's
registration statement filed under Section 12 of the Exchange Act, as amended,
including all amendments and reports filed for the purpose of updating such
description.

     In addition, all documents filed by the Company pursuant to Sections 13(a),
13(c), 14 or 15(d) of the Exchange Act after the date of this Prospectus and
prior to the termination of the offering contained herein shall be deemed to be
incorporated by reference into this Prospectus and to be a part hereof from the
date of filing of such documents.


           STOCKHOLDER REPORTS AND CURRENT SUPPLEMENTS TO PROSPECTUS

     Copies of the Company's Annual Report to Stockholders for its most recent
fiscal year will be furnished with this Prospectus. Participants in the Plan who
previously received a copy of such Annual Report may obtain an additional copy,
without charge, upon written request. Participants will receive copies of all
reports, proxy statements and communications distributed to all stockholders of
the Company.

     A current supplement to this Prospectus also will be furnished to all
participants in the Plan from time to time.  The supplement may provide current
information about the Committee members, the number of eligible and
participating employees and the options granted and outstanding under the Plan.
The supplement will be updated as appropriate to provide current information
about the Plan.  Changes in the information contained in this Prospectus, such
as amendments to the Plan and changes in the federal income tax consequences of
options, also may be included in the current supplement.

                                       11
<PAGE>
 
                                    EXPERTS

     The consolidated financial statements of Pitt-Des Moines, Inc.,
incorporated by reference in Pitt-Des Moines, Inc.'s Form 10-K for the year
ended 1997, have been audited by Ernst & Young LLP, independent auditors, as set
forth in their report thereon included therein and incorporated herein by
reference. Such consolidated financial statements are incorporated herein by
reference in reliance upon such report given upon the authority of such firm as
experts in accounting and auditing.


                                 LEGAL MATTERS

     The legality of the shares of Common Stock issued pursuant to the Plan has
been passed upon by Buchanan Ingersoll Professional Corporation, 20th Floor, One
Oxford Centre, 301 Grant Street, Pittsburgh, Pennsylvania 15219.


             DISCLOSURE OF COMMISSION POSITION ON INDEMNIFICATION
                        FOR SECURITIES ACT LIABILITIES

     Section 1743 of the Pennsylvania Business Corporation Law ("BCL") provides
mandatory indemnification for a Representative if he or she succeeds on the
merits or otherwise in the defense of any claim or action. The corporation must
indemnify him or her to the extent of his or her actual and reasonable expenses
(including attorney's fees) in connection with the claim or action.

     Section 1746(a) states that the statutory rights of indemnification shall
not be deemed exclusive of any other rights to which a person might be entitled
under any bylaw, agreement, or otherwise. However, 1746(b) forbids
indemnification to be made in any case where the act or

                                       12
<PAGE>
 
failure to act giving rise to the claim is determined by a court to be willful
misconduct or recklessness.

     The BCL, in Section 1747, also authorizes corporation to purchase and
maintain insurance on behalf of a Representative whether or not the corporation
would have the power to indemnify him or her.  Such insurance is declared to be
consistent with Pennsylvania's public policy.

     The Corporation's Bylaws provide that the Corporation shall indemnify
(including the advancement of expenses) to the full extent authorized or
permitted by law any current or former director or officer with respect to his
or her acts in that or related capacities.

     The Corporation's Bylaws provide that a director of the Corporation shall
not be personally liable for monetary damages for breach of fiduciary duty as a
director for any act or failure to act unless such breach or failure to perform
constitutes self dealing, willful misconduct or recklessness.  This limitation
on the personal liability of directors of the Corporation does not apply to the
responsibility or liability of a director pursuant to any criminal statute or
the liability of a director for the payment of taxes pursuant to local, state or
federal law.

     Policies of insurance are maintained by the Corporation under which the
directors and officers of the Corporation are insured, within the limits and
subject to the limitations of the policies, against certain expenses in
connection with the defense of actions, suits or proceedings, and certain
liabilities which might be imposed as a result of such actions, suits or
proceedings, to which they are parties by reason of being or having been such
directors or officers.

                                       13
<PAGE>
 
                                    PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.   Incorporation of Documents by Reference

          Pitt-Des Moines, Inc. (the "Corporation") hereby incorporates by
          reference into this Registration Statement the documents listed in (a)
          through (c) below. The Corporation also incorporates by reference,
          from the date of filing of such documents, all documents subsequently
          filed by it pursuant to Sections 13(a), 13(c), 14 and 15(d) of the
          Securities Exchange Act of 1934, as amended (the "Exchange Act"),
          prior to the filing of a post-effective amendment which indicates that
          all securities offered have been sold or which deregisters all
          securities then remaining unsold:

          (a)  The latest annual report of the Corporation filed pursuant to
               Section 13(a) or 15(d) under the Exchange Act;

          (b)  All other reports filed pursuant to Section 13(a) or 15(d) of the
               Exchange Act since the end of the fiscal year covered by the
               annual report referred to in (a) above; and

          (c)  The description of the Common Stock, no par value, of the
               Corporation contained in the Corporation's registration statement
               filed under Section 12 of the Exchange Act including any
               amendment or report filed for the purpose of updating such
               description.

Item 4.   Description of Securities

          Not applicable.

Item 5.   Interests of Named Experts and Counsel

          Not applicable.

Item 6.   Indemnification of Directors and Officers

          Pennsylvania statutory law regarding directors and officers insurance
          and indemnification is embodied in Subchapter D (Sections 1741 through
          1750) of the Pennsylvania Business Corporation Law of 1988, as amended
          (the "BCL"). Sections 1741 (relating to third party actions) and 1742
          (relating to derivative actions) of the BCL provide that, unless
          otherwise restricted by its bylaws, a business corporation shall have
          the power to indemnify any person who is made a party to a third-party
          or derivative action, respectively, by reason that such person is or
          was a representative of the corporation. The BCL defines
          representative to mean a director, officer, employee or agent thereof
          (a "Representative"). The sections further state that the corporation
          is authorized to indemnify the Representative against expenses
          (including attorneys' fees), judgments, fines and amounts paid in
          settlement actually and reasonably incurred by him or her in
          connection with the action. However, the Representative must have
          acted in good faith and with a reasonable belief that his or her
          actions were in the best interests, or not opposed to the best
          interests, of the corporation; and with respect to any criminal
          proceeding, the Representative must have had no reasonable cause to
          believe his or her conduct was unlawful.

          Section 1743 of the BCL provides mandatory indemnification for a
          Representative if he or she succeeds on the merits or otherwise in the
          defense of any claim or action. The corporation must
<PAGE>
 
          indemnify him or her to the extent of his or her actual and reasonable
          expenses (including attorney's fees) in connection with the claim or
          action.

          Section 1746(a) states that the statutory rights of indemnification
          shall not be deemed exclusive of any other rights to which a person
          might be entitled under any bylaw, agreement, or otherwise. However,
          1746(b) forbids indemnification to be made in any case where the act
          or failure to act giving rise to the claim is determined by a court to
          be willful misconduct or recklessness. A corporation may not provide
          indemnification in the case of willful misconduct or recklessness.

          The BCL, in Section 1747, also authorizes corporation to purchase and
          maintain insurance on behalf of a Representative whether or not the
          corporation would have the power to indemnify him or her. Such
          insurance is declared to be consistent with Pennsylvania's public
          policy.

          The Corporation's Bylaws provide that the Corporation shall indemnify
          (including the advancement of expenses) to the full extent authorized
          or permitted by law any current or former director or officer with
          respect to his or her acts in that or related capacities.

          The Corporation's Bylaws provide that a director of the Corporation
          shall not be personally liable for monetary damages for breach of
          fiduciary duty as a director for any act or failure to act unless such
          breach or failure to perform constitutes self dealing, willful
          misconduct or recklessness. This limitation on the personal liability
          of directors of the Corporation does not apply to the responsibility
          or liability of a director pursuant to any criminal statute or the
          liability of a director for the payment of taxes pursuant to local,
          state or federal law.

          Policies of insurance are maintained by the Corporation under which
          the directors and officers of the Corporation are insured, within the
          limits and subject to the limitations of the policies, against certain
          expenses in connection with the defense of actions, suits or
          proceedings, and certain liabilities which might be imposed as a
          result of such actions, suits or proceedings, to which they are
          parties by reason of being or having been such directors or officers.

Item 7.   Exemption From Registration Claimed

          Not applicable.

Item 8.   Exhibits

          5.1  Opinion of Buchanan Ingersoll Professional Corporation as to the
               legality of the Common Stock issued pursuant to the Plan (filed
               herewith)

          23.1 Consent of Independent Auditors, Ernst & Young LLP (filed
               herewith)
               
          23.2 Consent of Buchanan Ingersoll Professional Corporation (contained
               in their opinion filed as Exhibit 5.1 hereto)

          24.1 Powers of Attorney (filed herewith on the signature page)
<PAGE>
 
Item 9.   Undertakings

          The undersigned registrant hereby undertakes:

          1.   To file, during any period in which offers or sales are being
               made, a post-effective amendment to this Registration Statement
               to include any material information with respect to the plan of
               distribution not previously disclosed in this Registration
               Statement or any material change to such information in this
               Registration Statement.

          2.   That, for the purpose of determining any liability under the
               Securities Act of 1933, as amended (the "Securities Act"), each
               such post-effective amendment shall be deemed to be a new
               registration statement relating to the securities offered
               therein, and the offering of such securities at that time shall
               be deemed to be the initial bona fide offering thereof.

          3.   To remove from registration by means of a post-effective
               amendment any of the securities being registered which remain
               unsold at the termination of the offering.

          4.   That, for purposes of determining any liability under the
               Securities Act, each filing of the Corporation's annual report
               pursuant to Section 13(a) or Section 15(d) of the Exchange Act
               (and, where applicable, each filing of any employee benefit
               plan's annual report pursuant to Section 15(d) of the Exchange
               Act) that is incorporated by reference in this Registration
               Statement shall be deemed to be a new registration statement
               relating to the securities offered therein, and the offering of
               such securities at that time shall be deemed to be the initial
               bona fide offering thereof.

          5.   Insofar as indemnification for liabilities arising under the
               Securities Act may be permitted to directors, officers and
               controlling persons of the Corporation pursuant to the foregoing
               provisions, or otherwise, the registrant has been advised that in
               the opinion of the Securities and Exchange Commission such
               indemnification is against public policy as expressed in the Act
               and is, therefore, unenforceable. In the event that a claim for
               indemnification against such liabilities (other than the payment
               by the registrant of expenses incurred or paid by a director,
               officer or controlling person of the registrant in the successful
               defense of any action, suit or proceeding) is asserted by such
               director, officer or controlling person in connection with the
               securities being registered, the registrant will, unless in the
               opinion of its counsel the matter has been settled by controlling
               precedent, submit to a court of appropriate jurisdiction the
               question whether such indemnification by it is against public
               policy as expressed in the Act and will be governed by the final
               adjudication of such issue.
<PAGE>
 
                                  SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-8 and has duly caused this Registration Statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in The
Woodlands, Texas on December 14, 1998.

                                                      PITT-DES MOINES, INC.



   December 14, 1998                                  By: /s/ Wm. W. McKee
                                                         -----------------------
                                                            Wm. W. McKee
                                                            President
                                                         Chief Executive Officer

KNOW ALL MEN BY THESE PRESENTS that each person whose signature appears below
constitutes and appoints Wm. W. McKee, R. A. Byers and P. O. Elbert, each of
them, such person's true and lawful attorneys-in-fact and agents, with full
power of substitution and revocation, for such person and in such person's name,
place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments to this Registration Statement) and to file
the same with all exhibits thereto, and other documents in connection therewith,
with the Securities and Exchange Commission, granting unto said attorneys-in-
fact and agents, and each of them, full power and authority to do and perform
each and every act and things requisite and necessary to be done, as fully to
all intents and purposes as such person might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents or any of
them, or their or his substitute or substitutes, may lawfully do or cause to be
done by virtue thereof.

Pursuant to the requirements of the Securities Act, this Registration Statement
has been signed below by the following persons on behalf of the Registrant and
in the capacities and on the dates indicted.

  SIGNATURES                      TITLE                     DATE

PRINCIPAL EXECUTIVE OFFICER AND DIRECTOR:


      /s/ Wm. W. McKee            President, Chief          November 24, 1998
-----------------------------     Executive Officer and
          Wm. W. McKee            Director


PRINCIPAL FINANCIAL AND ACCOUNTING OFFICER:



      /s/ R. A. Byers             Chief Financial Officer   November 24, 1998
-----------------------------     and Chief Accounting
          R. A. Byers             Officer
<PAGE>
 
                             SIGNATURES  (Cont'd)

  SIGNATURES                      TITLE                     DATE

OTHER DIRECTORS:


      /s/ J. C. Bates             Director                  November 24, 1998
-----------------------------
          J. C. Bates



      /s/ V. G. Beghini           Director                  November 24, 1998
-----------------------------
          V. G. Beghini



      /s/ R. W. Dean              Director                  November 24, 1998
-----------------------------
          R. W. Dean



      /s/ P. O. Elbert            Director                  November 24, 1998
-----------------------------
          P. O. Elbert



      /s/ W. R. Jackson           Director                  November 30, 1998
-----------------------------
          W. R. Jackson



      /s/ W. R. Jackson, Jr.      Director                  November 30, 1998
-----------------------------
          W. R. Jackson, Jr.



      /s/ W. E. Lewellen          Director                  November 28, 1998
-----------------------------
          W. E. Lewellen



      /s/ A. J. Paddock           Director                  November 30, 1998
-----------------------------
          A. J. Paddock



      /s/ J. W. Robinson          Director                  November 24, 1998
-----------------------------
          J. W. Robinson



      /s/ P. J. Townsend          Director                  December 2, 1998
-----------------------------
          P. J. Townsend
<PAGE>
 
                                 Exhibit Index


  5.1     Opinion of Buchanan Ingersoll Professional Corporation as to the
          legality of the Common Stock issued pursuant to the Plan (filed
          herewith)

 23.1     Consent of Independent Auditors, Ernst & Young LLP (filed herewith)

 23.2     Consent of Buchanan Ingersoll Professional Corporation (contained in
          their opinion filed as Exhibit 5.1 hereto)

 24.1     Powers of Attorney (filed herewith on the signature page)
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 46266}]
{"company-data": {"conformed-name": "PITT DES MOINES INC", "cik": "0000078853", "assigned-sic": "3443", "irs-number": "250729430", "state-of-incorporation": "PA", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-68853", "film-number": "98768970"}, "business-address": {"street1": "3400 GRAND AVE", "city": "PITTSBURGH", "state": "PA", "zip": "15225", "phone": "4123313000"}, "mail-address": {"street1": "PITT DES MOINES INC", "street2": "3400 GRAND AVENUE", "city": "PITTSBURGH", "state": "PA", "zip": "15225"}, "former-company": [{"former-conformed-name": "PITTSBURGH DES MOINES CORP", "date-changed": "19850908"}, {"former-conformed-name": "PITTSBURGH DES MOINES STEEL CO", "date-changed": "19810325"}]}
SECURITIES AND EXCHANGE COMMISSION

                            Washington, D.C.  20549

                                   FORM S-8

                         REGISTRATION STATEMENT UNDER
                          THE SECURITIES ACT OF 1933

                             PITT-DES MOINES, INC.
            (Exact name of registrant as specified in its charter)

Commonwealth of Pennsylvania                                      25-0729430
(State or other jurisdiction of                                 (IRS Employer
incorporation or organization)                               Identification No.)

10200 Grogan's Mill Road,  The Woodlands, Texas                      77380
   (Address of Principal Executive Offices)                        (Zip Code)

                             PITT-DES MOINES, INC.
                    LONG TERM INCENTIVE STOCK PLAN OF 1997
                           (Full title of the plan)

               R. A. Byers, Vice President Finance and Treasurer
                             Pitt-Des Moines, Inc.
                      10200 Grogan's Mill Road, Suite 300
                          The Woodlands, Texas  77380
                    (Name and address of agent for service)

                                (281) 774-2200
         (Telephone number, including area code, of agent for service)

                        CALCULATION OF REGISTRATION FEE
============================================================================================================================
                                                        Proposed                   Proposed
      Title of                    Amount to             maximum                     maximum                   Amount of
   securities to be                   be             offering price                aggregate                 registration
     registered                   registered           per share                 offering price                  fee
---------------------------     ---------------     ----------------          ---------------------        -----------------
Common Stock                   706,000             $17.56(1)                 $12,397,360 (1)               $3,446.47
    (no par value)                 shares
   Common Stock                   694,000             $23.25(2)                 $16,135,500 (2)               $4,485.67
    (no par value)                 shares
      TOTALS                    1,400,000                 -                              -                    $7,932.14
                                   shares
============================================================================================================================
(1)  Estimated solely for purposes of calculating the registration fee pursuant
     to Rule 457(h).  The price is the exercise price of the stock options
     granted to date.

(2)  Estimated solely for purposes of calculating the registration fee pursuant
     to Rule 457(h). The price has been determined in accordance with
     Rule 457(c) which is the average of the high and low prices of the Common
     Stock on the American Stock Exchange on December 11, 1998.
PROSPECTUS
----------

                             PITT-DES MOINES, INC.

                    LONG TERM INCENTIVE STOCK PLAN OF 1997

                       1,400,000 SHARES OF COMMON STOCK

     This Prospectus relates to up to 1,400,000 shares of our common stock, no
par value (the "Common Stock") which are being offered pursuant to the Pitt-Des
Moines, Inc. Long Term Incentive Stock Plan of 1997 (the "Plan") described
herein.

     You may receive shares of our Common Stock under the Plan from a restricted
stock grant or stock option grant made to you.

     This Prospectus cannot be used to reoffer or resale the Common Stock you
may acquire under the Plan.

     Our Common Stock is traded on the American Stock Exchange.

     If you do not already have our latest Annual Report, we will provide it
with the Prospectus.

     Neither the Securities and Exchange Commission nor any other state
securities commission has approved or disapproved of these securities or passed
upon the accuracy or adequacy of this prospectus.  Any representation to the
contrary is a criminal offense.

--------------------------------------------------------------------------------

                             PITT-DES MOINES, INC.

                      10200 GROGAN'S MILL ROAD, SUITE 300
                           THE WOODLANDS, TX  77380
                                 281-774-2200

               THE DATE OF THIS PROSPECTUS IS DECEMBER 11, 1998.

                THIS DOCUMENT CONSTITUTES PART OF A PROSPECTUS
                 COVERING SECURITIES THAT HAVE BEEN REGISTERED
                       UNDER THE SECURITIES ACT OF 1933.
CONTENTS

                                                                       Page
                                                                       ----

Availability of Additional Information About the Company................iii
General Information.....................................................  1
Description of the Plan.................................................  2
     1.  Administration.................................................  2
     2.  Eligibility and Participation..................................  2
     3.  Shares Available for Issuance..................................  3
     4.  Types of Grants................................................  3
     5.  Option Price...................................................  3
     6.  Option Period, Exercise........................................  4
     7.  Restricted Stock...............................................  5
     8.  No Right to Employment.........................................  5
     9.  Tax Withholding................................................  6
    10.  Payment........................................................  6
    11.  Options Not Transferable.......................................  6
    12.  Surrender of Options, Return of Shares.........................  7
    13.  Adjustment in Number, Price of Shares..........................  7
    14.  Amendment, Discontinuance, Term, Assignment....................  8
Certain Federal Income Tax Consequences.................................  8
Restrictions on Reoffers and Resales.................................... 10
Incorporation of Certain Documents by Reference......................... 10
Stockholder Reports and Current Supplements to Prospectus............... 11
Experts................................................................. 12
Legal Matters........................................................... 12

                                      ii
AVAILABILITY OF ADDITIONAL INFORMATION ABOUT THE COMPANY

     We are subject to the Securities and Exchange Act of 1934, as amended (the
"Exchange Act"), and file reports, proxy statements and other information with
the Securities and Exchange Commission (the "Commission").

     Those documents can be inspected and copied at the Public Reference Section
of the Commission at Judiciary Plaza, 450 Fifth Street, N.W., Washington, D.C.
20549; and at the Commission's regional offices at Northwestern Atrium Center,
500 West Madison Street, Suite 1400, Chicago, Illinois 60661-2511; and Seven
World Trade Center, 13th Floor, New York, New York 10048.  Copies of this
material can also be obtained at prescribed rates from the Public Reference
Section of the Commission at Judiciary Plaza, 450 Fifth Street, N.W.,
Washington, D.C. 20549.  Reports, proxy statements and other information
concerning the Company may also be inspected at the offices of the American
Stock Exchange.

     We have filed with the Commission a Registration Statement on Form S-8
(herein, together with all amendments and exhibits thereto, referred to as the
"Registration Statement") under the Securities Act of 1933, as amended (the
"Securities Act"), for our Common Stock and the Plan.  This Prospectus does not
contain all of the information in the Registration Statement and its exhibits;
certain parts have been omitted in accordance with the Commission's rules and
regulations. You may refer to the Registration Statement for further
information.  The Registration Statement, including exhibits, may be inspected
without charge and copied at the Public Reference Section of the Commission at
450 Fifth Street, N.W., Washington, D.C. 20549, and at the regional offices of
the Commission described above.  Electronic registration

                                      iii
statements made through the Electronic Data Gathering Analysis and Retrieval
(EDGAR) system are publicly available through the Commission's web site 
(http://www.sec.gov).

     We will provide you free, upon request, a copy of any information
incorporated by reference in Item 3 of Part II of the Registration Statement.
These documents are incorporated herein by reference.  Requests for copies and
additional information about the Plan and its administrator should be directed
to Pitt-Des Moines, Inc., 10200 Grogan's Mill Road, Suite 300, The Woodlands,
Texas 77380, Attention: R. A. Byers, Vice President, Finance and Treasurer,
(281) 774-2200.  We will also provide you free, upon request, a copy of any
documents required to be delivered to you by Rule 428(b) under the Securities
Act.

--------------------------------------------------------------------------------

     You should rely only on the information contained in this document or
others that we have referred you to.  We have not authorized anyone to provide
you with information that is different from that contained in this Prospectus.
The information contained in this Prospectus is accurate only as of the date of
the information contained in this Prospectus, regardless of the time of delivery
of this Prospectus or of any sale of the Common Stock.

                                      iv
PITT-DES MOINES, INC.

                    LONG TERM INCENTIVE STOCK PLAN OF 1997
                              
                              GENERAL INFORMATION

     Pitt-Des Moines, Inc. (the "Company"), 10200 Grogan's Mill Road, The
Woodlands, Texas 77380, (281-774-2200), is the sponsoring employer and issuer of
shares of common stock, no par value (the "Common Stock") that may be granted to
or purchased by eligible employees of the Company and its Subsidiaries under the
Pitt-Des Moines, Inc. Long Term Incentive Stock Plan of 1997 (the "Plan").  The
Plan was adopted by the Board of Directors of the Company on November 6, 1997,
subject to approval by the stockholders of the Company which was obtained on
May 7, 1998. The number of shares of the Company's Common Stock that may be
granted or purchased under the Plan is 1,400,000 shares. All shares or options
granted under the Plan must be granted not later than November 1, 2007.

     The purpose of the Plan is to promote the long-term growth and
profitability of the Company by providing certain officers and key employees of
the Company and its Subsidiaries with incentives to maximize stockholder value,
otherwise contribute to the success of the Company and enable the Company to
attract, retain and reward the best available persons for positions of
substantial responsibility, all as determined by the Committee in its
administration of the Plan.  The Plan is not subject to the provisions of the
Employee Retirement Income Security Act of 1974.

                                       1
DESCRIPTION OF THE PLAN

     The following description is intended to summarize provisions of the Plan.
It is not a complete statement of the Plan or its operation and is qualified in
its entirety by reference to the complete text of the Plan.  Prospective
participants should become familiar with the text of the Plan.  A current copy
of the Plan is on file with the Secretary of the Company and may be reviewed by
participants or prospective participants in the Plan upon request.  Unless
defined in this Prospectus, each capitalized term used below is defined and has
the meaning ascribed to it in the Plan.

1.   ADMINISTRATION

     The Plan will be administered by a committee (the "Committee") consisting
of at least three directors of the Company who will be appointed by and serve at
the pleasure of the Board of Directors.  Subject to the terms of the Plan, the
Committee will select from eligible employees those persons to whom options and
restricted stock will be granted, the number of shares to be included in each
grant or option, the option price and the period during which each option may be
exercised and during which each grant and/or option may vest.

2.   ELIGIBILITY

     Options and shares of restricted stock may be granted under the Plan to
officers and key employees of the Company and its Subsidiaries (including
officers and employees who are directors of the Company) who, in the opinion of
the Committee, are mainly responsible for the continued growth, development and
future financial success of the business of the Company. As

                                       2
of the date of this Prospectus, there are approximately 9 officers and key
employees of the Company and its Subsidiaries who may be eligible generally to
participate under the Plan.

3.   SHARES AVAILABLE FOR ISSUANCE

     The total number of shares which may be issued pursuant to the Plan is
1,400,000 shares of the Common Stock of the Company.  The shares may be either
authorized and unissued shares or shares held in the treasury of the Company.
This number of shares is subject to adjustment to prevent dilution or
enlargement of rights under the Plan.  Shares covered by options or restricted
stock granted under the Plan that terminate or expire without being exercised
will remain available for the granting of future shares of restricted stock or
options under the Plan.  All shares of restricted stock or options granted under
the Plan must be granted before November 1, 2007.

4.   TYPES OF GRANTS

     The Plan provides for the Committee, in its discretion, to grant only
shares of restricted stock or options which are Non-Qualified Stock Options
under the Internal Revenue Code.  See "Certain Federal Income Tax Consequences"
below for a summary of the differing tax consequences for Non-Qualified Stock
Options and grants of restricted stock.

5.   OPTION PRICE

     The price at which each share covered by an option granted under the Plan
may be purchased will be determined in each case by the Committee but shall not
be less than the fair

                                       3
market value of the share at the time the option is granted. Fair market value
is defined in the Plan to be the average of the high and low sales prices per
share for the Common Stock of the Company as reported on the stock exchange on
which the stock is traded on the date immediately preceding the relevant date
under the Plan or, if no sales were made on that date, on the closest preceding
date on which there were sales reports. On December 11, 1998, such fair market
value for the Company's Common Stock was $23.25 per share.

6.   OPTION PERIOD AND EXERCISE OF OPTIONS

     An option may be exercised in whole at any time or in part from time to
time within such period as may be determined by the Committee provided that the
option period may not exceed ten (10) years from the granting of the option. If
the optionee ceases to be employed by the Company or any of its subsidiaries for
any reason other than death, disability, Deferred Retirement (retirement past
age 65), Normal Retirement (retirement at age 65) or Early Retirement
(retirement before age 65), the option may be exercised only within 90 days
after termination of optionee's employment (unless termination is for Cause in
which case the option expires immediately upon termination). A termination for
Cause is when employment is terminated for committing a crime, disloyalty,
grossly negligence performance or the like. In the event of optionee's death,
disability or Early Retirement, the option may be exercised within 1 year after
the date of death, disability or Early Retirement. Should optionee take Deferred
Retirement or Normal Retirement, the option may be exercised within 3 years from
the date of optionee's Deferred Retirement or Normal Retirement.

                                       4
7.   RESTRICTED STOCK

     Grants of restricted stock may be made by the Committee from time to time
pursuant to the Plan, such grants being subject to such restrictions as the
Committee deems appropriate, provided that in no event shall any grants of
restricted stock vest more than ten years after the date of grant.  Except as
otherwise provided by the Committee, from and after the date of grant, during
periods of restriction or otherwise, shares granted as restricted stock shall
have all of the rights of a holder of Common Stock, including but not limited to
the rights to vote and receive dividends.

8.   NO RIGHT TO CONTINUED EMPLOYMENT

     In consideration for each grant of an option or restricted stock, the
optionee (or grantee as the case may be) shall agree to remain in the employment
of the Company or a Subsidiary for at least one (1) year from the date of the
grant.  Nothing contained in the Plan nor in any stock option agreement or
agreement concerning restricted stock shall confer upon any grantee or optionee
any right with respect to the continuance of employment by the Company or any of
its Subsidiaries nor interfere in any way with the right of the Company or any
Subsidiary to terminate his or her employment or change his or her compensation
at any time.

                                       5
9.   TAX WITHHOLDING

     Prior to the delivery of certificates for shares to be issued under the
Plan the Company has the right to require the grantee or optionee to remit to
the Company an amount sufficient to satisfy required income tax withholding.

10.  PAYMENT

     The price of each share purchased pursuant to an option shall be paid in
full at the time of each exercise of the option by any combination of the
following:  (i) in cash; (ii) by delivery of Common Stock with a Fair Market
Value equal to the Exercise Price; (iii) by delivery of irrevocable instructions
of sale to a broker on terms satisfactory to the Company to pay the Exercise
Price; or (iv) by authorizing the Company to withhold Common Stock with a Fair
Market Value equal to the Exercise Price.  Participants will not be required to
pay the Company consideration for grants of restricted stock.

11.  OPTIONS NOT TRANSFERABLE

     Options are not transferable by the optionee except by qualified domestic
relation's order or by will or the laws of descent and distribution.  During the
lifetime of the optionee, options may be exercised only by the optionee or by
his or her guardian or legal representative.

                                       6
12.  SURRENDER OF OPTIONS, RETURN OF RESTRICTED SHARES

     The Committee, in its sole discretion, may permit an optionee voluntarily
to surrender for cancellation an option granted under the Plan, such surrender
to be conditioned upon the granting to such optionee of a new option under the
Plan for the same or a different number of shares as the option surrendered, or
may require such voluntary surrender as a condition precedent to the grant of a
new option to such optionee.  Any such new option shall be exercisable at the
price, during the period, and in accordance with any other terms and conditions
specified by the Committee at the time the new option is granted, all determined
in accordance with the provisions of the Plan without regard to the price,
period of exercise, or any other terms or conditions of the option surrendered
for cancellation.  Shares covered by options granted under the Plan and
subsequently surrendered for cancellation would again be available for the
granting of options or as grants of restricted stock under the Plan.  In the
event that the conditions for vesting of any option or restricted shares shall
fail to occur, any shares subject to such unvested option or restricted shares
returned by reason of the failure to vest, would again be available for the
granting of options or as grants of restricted stock under the Plan.

13.  ADJUSTMENT OF NUMBER AND PRICE OF SHARES

     The Plan contains provisions with respect to the adjustment of the number,
kind and price of shares covered by options or restricted stock agreements, and
the number of shares subject to the Plan which are not covered by restricted
stock agreements or options as the result of stock dividends, reorganization,
recapitalization, stock split-up, combination of shares, merger or consolidation
and other corporate changes.

                                       7
14.  AMENDMENT OR DISCONTINUANCE

     The Board of Directors may alter, amend, suspend or discontinue the Plan,
provided that no such action shall deprive any person, without such person's
consent, of any rights previously granted pursuant to the Plan.

                    CERTAIN FEDERAL INCOME TAX CONSEQUENCES

     Under existing federal income tax laws, an employee who receives a stock
option or shares of restricted stock under the Plan which are subject to
restrictions which create a Substantial Risk of Forfeiture (as defined under
Section 83 of the Internal Revenue Code) will not normally realize any income
with respect to the stock option or restricted stock, nor will the Company be
allowed to take a corresponding deduction for federal income tax purposes, in
the year of the grant or award.

     When a non-qualified stock option granted pursuant to the Plan is
exercised, the option-holder will realize ordinary income measured by the
difference between the aggregate exercise price of the shares of Common Stock
underlying the option which is exercised, and the aggregate fair market value of
such shares of Common Stock on the exercise date. The Company will be entitled
to take a federal income tax deduction equal to the amount the employee is
required to treat as ordinary income.

     An employee who receives restricted stock subject to restrictions which
create a Substantial Risk of Forfeiture will normally realize taxable income on
the date the shares of restricted stock become transferable or are no longer
subject to Substantial Risk of Forfeiture. The amount of such taxable income
will be equal to the amount by which the fair market value

                                       8
of the shares of Common Stock on the date such restrictions lapse (or any
earlier date on which the shares become transferable) exceeds their purchase
price, if any. An employee may elect within thirty (30) days of any grant,
however, to include in income in the year of grant the excess of the fair market
value of the shares of Common Stock (without regard to any restrictions) on the
date of grant over their purchase price, if any.

     Any income from the restricted stock, i.e., dividends, received by the
employee constitutes additional compensation and will be included in the
employee's gross income for the year when the income is received, subject to
withholding.  If any employee makes the above election to include in the year of
grant the excess of the fair market value of shares of Common Stock over their
purchase price, then any income from the restricted shares during the period of
restrictions would be dividend income and not additional compensation.

     Upon accelerated exercisability of options and accelerated lapsing of
restrictions on restricted stock in connection with a change in control of the
Company, certain amounts associated with such awards could, depending upon the
individual circumstances of the participant, constitute "excess parachute
payments" under the golden parachute provisions of the Internal Revenue Code.
Pursuant to these provisions a participant will be subject to a 20% excise tax
on any excess parachute payment and the Company will be denied any deduction
with respect to such excess parachute payment.  The limit on the Company's
deductibility of compensation under Section 162(m) of the Internal Revenue Code
is also reduced by the amount of any excess parachute payments.  Whether amounts
constitute excess parachute payments depends upon, among other things, the value
of the awards accelerated and the past compensation of the participant.

                                       9
RESTRICTIONS ON REOFFERS AND RESALES

     This Prospectus will not be available for reoffers or resales of Common
Stock acquired by "affiliates" of the Company or any Subsidiary under the Plan.
Directors, officers and control persons of the Company may be considered
"affiliates" of the Company and, as such, may transfer shares of Common Stock,
including shares purchased through the Plan, only in compliance with the
registration requirements of the Securities Act of 1933, as amended (the "Act"),
or in compliance with an exemption therefrom. Generally, in the absence of
registration under the Act, shares of Common Stock held by such persons may be
sold pursuant to an available exemption from the registration requirement of the
Act such as Rule 144 of the Commission. Grantees and optionees who may be
"affiliates" are urged to consult legal counsel prior to any proposed sale of
Common Stock. Consistent with the provisions of the Act, the Company may place a
restrictive legend on Common Stock issued to such persons and issue stop order
instructions to the Company's transfer agent.

                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

     The following documents filed with the Securities and Exchange Commission
are incorporated by reference in this Prospectus:

     1.   The Company's latest Annual Report on Form 10-K filed pursuant to
Section 13 or 15(d) of the Securities Exchange Act of 1934 ("Exchange Act");

     2.   All other reports filed pursuant to Section 13(a) or 15(d) of the
Exchange Act, as amended, since December 31, 1997; and

                                       10
3.   The description of the Common Stock contained in the Company's
registration statement filed under Section 12 of the Exchange Act, as amended,
including all amendments and reports filed for the purpose of updating such
description.

     In addition, all documents filed by the Company pursuant to Sections 13(a),
13(c), 14 or 15(d) of the Exchange Act after the date of this Prospectus and
prior to the termination of the offering contained herein shall be deemed to be
incorporated by reference into this Prospectus and to be a part hereof from the
date of filing of such documents.

           STOCKHOLDER REPORTS AND CURRENT SUPPLEMENTS TO PROSPECTUS

     Copies of the Company's Annual Report to Stockholders for its most recent
fiscal year will be furnished with this Prospectus. Participants in the Plan who
previously received a copy of such Annual Report may obtain an additional copy,
without charge, upon written request. Participants will receive copies of all
reports, proxy statements and communications distributed to all stockholders of
the Company.

     A current supplement to this Prospectus also will be furnished to all
participants in the Plan from time to time.  The supplement may provide current
information about the Committee members, the number of eligible and
participating employees and the options granted and outstanding under the Plan.
The supplement will be updated as appropriate to provide current information
about the Plan.  Changes in the information contained in this Prospectus, such
as amendments to the Plan and changes in the federal income tax consequences of
options, also may be included in the current supplement.

                                       11
EXPERTS

     The consolidated financial statements of Pitt-Des Moines, Inc.,
incorporated by reference in Pitt-Des Moines, Inc.'s Form 10-K for the year
ended 1997, have been audited by Ernst & Young LLP, independent auditors, as set
forth in their report thereon included therein and incorporated herein by
reference. Such consolidated financial statements are incorporated herein by
reference in reliance upon such report given upon the authority of such firm as
experts in accounting and auditing.

                                 LEGAL MATTERS

     The legality of the shares of Common Stock issued pursuant to the Plan has
been passed upon by Buchanan Ingersoll Professional Corporation, 20th Floor, One
Oxford Centre, 301 Grant Street, Pittsburgh, Pennsylvania 15219.

             DISCLOSURE OF COMMISSION POSITION ON INDEMNIFICATION
                        FOR SECURITIES ACT LIABILITIES

     Section 1743 of the Pennsylvania Business Corporation Law ("BCL") provides
mandatory indemnification for a Representative if he or she succeeds on the
merits or otherwise in the defense of any claim or action. The corporation must
indemnify him or her to the extent of his or her actual and reasonable expenses
(including attorney's fees) in connection with the claim or action.

     Section 1746(a) states that the statutory rights of indemnification shall
not be deemed exclusive of any other rights to which a person might be entitled
under any bylaw, agreement, or otherwise. However, 1746(b) forbids
indemnification to be made in any case where the act or

                                       12
failure to act giving rise to the claim is determined by a court to be willful
misconduct or recklessness.

     The BCL, in Section 1747, also authorizes corporation to purchase and
maintain insurance on behalf of a Representative whether or not the corporation
would have the power to indemnify him or her.  Such insurance is declared to be
consistent with Pennsylvania's public policy.

     The Corporation's Bylaws provide that the Corporation shall indemnify
(including the advancement of expenses) to the full extent authorized or
permitted by law any current or former director or officer with respect to his
or her acts in that or related capacities.

     The Corporation's Bylaws provide that a director of the Corporation shall
not be personally liable for monetary damages for breach of fiduciary duty as a
director for any act or failure to act unless such breach or failure to perform
constitutes self dealing, willful misconduct or recklessness.  This limitation
on the personal liability of directors of the Corporation does not apply to the
responsibility or liability of a director pursuant to any criminal statute or
the liability of a director for the payment of taxes pursuant to local, state or
federal law.

     Policies of insurance are maintained by the Corporation under which the
directors and officers of the Corporation are insured, within the limits and
subject to the limitations of the policies, against certain expenses in
connection with the defense of actions, suits or proceedings, and certain
liabilities which might be imposed as a result of such actions, suits or
proceedings, to which they are parties by reason of being or having been such
directors or officers.

                                       13
PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.   Incorporation of Documents by Reference

          Pitt-Des Moines, Inc. (the "Corporation") hereby incorporates by
          reference into this Registration Statement the documents listed in (a)
          through (c) below. The Corporation also incorporates by reference,
          from the date of filing of such documents, all documents subsequently
          filed by it pursuant to Sections 13(a), 13(c), 14 and 15(d) of the
          Securities Exchange Act of 1934, as amended (the "Exchange Act"),
          prior to the filing of a post-effective amendment which indicates that
          all securities offered have been sold or which deregisters all
          securities then remaining unsold:

          (a)  The latest annual report of the Corporation filed pursuant to
               Section 13(a) or 15(d) under the Exchange Act;

          (b)  All other reports filed pursuant to Section 13(a) or 15(d) of the
               Exchange Act since the end of the fiscal year covered by the
               annual report referred to in (a) above; and

          (c)  The description of the Common Stock, no par value, of the
               Corporation contained in the Corporation's registration statement
               filed under Section 12 of the Exchange Act including any
               amendment or report filed for the purpose of updating such
               description.

Item 4.   Description of Securities

          Not applicable.

Item 5.   Interests of Named Experts and Counsel

          Not applicable.

Item 6.   Indemnification of Directors and Officers

          Pennsylvania statutory law regarding directors and officers insurance
          and indemnification is embodied in Subchapter D (Sections 1741 through
          1750) of the Pennsylvania Business Corporation Law of 1988, as amended
          (the "BCL"). Sections 1741 (relating to third party actions) and 1742
          (relating to derivative actions) of the BCL provide that, unless
          otherwise restricted by its bylaws, a business corporation shall have
          the power to indemnify any person who is made a party to a third-party
          or derivative action, respectively, by reason that such person is or
          was a representative of the corporation. The BCL defines
          representative to mean a director, officer, employee or agent thereof
          (a "Representative"). The sections further state that the corporation
          is authorized to indemnify the Representative against expenses
          (including attorneys' fees), judgments, fines and amounts paid in
          settlement actually and reasonably incurred by him or her in
          connection with the action. However, the Representative must have
          acted in good faith and with a reasonable belief that his or her
          actions were in the best interests, or not opposed to the best
          interests, of the corporation; and with respect to any criminal
          proceeding, the Representative must have had no reasonable cause to
          believe his or her conduct was unlawful.

          Section 1743 of the BCL provides mandatory indemnification for a
          Representative if he or she succeeds on the merits or otherwise in the
          defense of any claim or action. The corporation must
indemnify him or her to the extent of his or her actual and reasonable
          expenses (including attorney's fees) in connection with the claim or
          action.

          Section 1746(a) states that the statutory rights of indemnification
          shall not be deemed exclusive of any other rights to which a person
          might be entitled under any bylaw, agreement, or otherwise. However,
          1746(b) forbids indemnification to be made in any case where the act
          or failure to act giving rise to the claim is determined by a court to
          be willful misconduct or recklessness. A corporation may not provide
          indemnification in the case of willful misconduct or recklessness.

          The BCL, in Section 1747, also authorizes corporation to purchase and
          maintain insurance on behalf of a Representative whether or not the
          corporation would have the power to indemnify him or her. Such
          insurance is declared to be consistent with Pennsylvania's public
          policy.

          The Corporation's Bylaws provide that the Corporation shall indemnify
          (including the advancement of expenses) to the full extent authorized
          or permitted by law any current or former director or officer with
          respect to his or her acts in that or related capacities.

          The Corporation's Bylaws provide that a director of the Corporation
          shall not be personally liable for monetary damages for breach of
          fiduciary duty as a director for any act or failure to act unless such
          breach or failure to perform constitutes self dealing, willful
          misconduct or recklessness. This limitation on the personal liability
          of directors of the Corporation does not apply to the responsibility
          or liability of a director pursuant to any criminal statute or the
          liability of a director for the payment of taxes pursuant to local,
          state or federal law.

          Policies of insurance are maintained by the Corporation under which
          the directors and officers of the Corporation are insured, within the
          limits and subject to the limitations of the policies, against certain
          expenses in connection with the defense of actions, suits or
          proceedings, and certain liabilities which might be imposed as a
          result of such actions, suits or proceedings, to which they are
          parties by reason of being or having been such directors or officers.

Item 7.   Exemption From Registration Claimed

          Not applicable.

Item 8.   Exhibits

          5.1  Opinion of Buchanan Ingersoll Professional Corporation as to the
               legality of the Common Stock issued pursuant to the Plan (filed
               herewith)

          23.1 Consent of Independent Auditors, Ernst & Young LLP (filed
               herewith)
               
          23.2 Consent of Buchanan Ingersoll Professional Corporation (contained
               in their opinion filed as Exhibit 5.1 hereto)

          24.1 Powers of Attorney (filed herewith on the signature page)
Item 9.   Undertakings

          The undersigned registrant hereby undertakes:

          1.   To file, during any period in which offers or sales are being
               made, a post-effective amendment to this Registration Statement
               to include any material information with respect to the plan of
               distribution not previously disclosed in this Registration
               Statement or any material change to such information in this
               Registration Statement.

          2.   That, for the purpose of determining any liability under the
               Securities Act of 1933, as amended (the "Securities Act"), each
               such post-effective amendment shall be deemed to be a new
               registration statement relating to the securities offered
               therein, and the offering of such securities at that time shall
               be deemed to be the initial bona fide offering thereof.

          3.   To remove from registration by means of a post-effective
               amendment any of the securities being registered which remain
               unsold at the termination of the offering.

          4.   That, for purposes of determining any liability under the
               Securities Act, each filing of the Corporation's annual report
               pursuant to Section 13(a) or Section 15(d) of the Exchange Act
               (and, where applicable, each filing of any employee benefit
               plan's annual report pursuant to Section 15(d) of the Exchange
               Act) that is incorporated by reference in this Registration
               Statement shall be deemed to be a new registration statement
               relating to the securities offered therein, and the offering of
               such securities at that time shall be deemed to be the initial
               bona fide offering thereof.

          5.   Insofar as indemnification for liabilities arising under the
               Securities Act may be permitted to directors, officers and
               controlling persons of the Corporation pursuant to the foregoing
               provisions, or otherwise, the registrant has been advised that in
               the opinion of the Securities and Exchange Commission such
               indemnification is against public policy as expressed in the Act
               and is, therefore, unenforceable. In the event that a claim for
               indemnification against such liabilities (other than the payment
               by the registrant of expenses incurred or paid by a director,
               officer or controlling person of the registrant in the successful
               defense of any action, suit or proceeding) is asserted by such
               director, officer or controlling person in connection with the
               securities being registered, the registrant will, unless in the
               opinion of its counsel the matter has been settled by controlling
               precedent, submit to a court of appropriate jurisdiction the
               question whether such indemnification by it is against public
               policy as expressed in the Act and will be governed by the final
               adjudication of such issue.
SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-8 and has duly caused this Registration Statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in The
Woodlands, Texas on December 14, 1998.

                                                      PITT-DES MOINES, INC.

   December 14, 1998                                  By: /s/ Wm. W. McKee
                                                         -----------------------
                                                            Wm. W. McKee
                                                            President
                                                         Chief Executive Officer

KNOW ALL MEN BY THESE PRESENTS that each person whose signature appears below
constitutes and appoints Wm. W. McKee, R. A. Byers and P. O. Elbert, each of
them, such person's true and lawful attorneys-in-fact and agents, with full
power of substitution and revocation, for such person and in such person's name,
place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments to this Registration Statement) and to file
the same with all exhibits thereto, and other documents in connection therewith,
with the Securities and Exchange Commission, granting unto said attorneys-in-
fact and agents, and each of them, full power and authority to do and perform
each and every act and things requisite and necessary to be done, as fully to
all intents and purposes as such person might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents or any of
them, or their or his substitute or substitutes, may lawfully do or cause to be
done by virtue thereof.

Pursuant to the requirements of the Securities Act, this Registration Statement
has been signed below by the following persons on behalf of the Registrant and
in the capacities and on the dates indicted.

  SIGNATURES                      TITLE                     DATE

PRINCIPAL EXECUTIVE OFFICER AND DIRECTOR:

      /s/ Wm. W. McKee            President, Chief          November 24, 1998
-----------------------------     Executive Officer and
          Wm. W. McKee            Director

PRINCIPAL FINANCIAL AND ACCOUNTING OFFICER:

      /s/ R. A. Byers             Chief Financial Officer   November 24, 1998
-----------------------------     and Chief Accounting
          R. A. Byers             Officer
SIGNATURES  (Cont'd)

  SIGNATURES                      TITLE                     DATE

OTHER DIRECTORS:

      /s/ J. C. Bates             Director                  November 24, 1998
-----------------------------
          J. C. Bates

      /s/ V. G. Beghini           Director                  November 24, 1998
-----------------------------
          V. G. Beghini

      /s/ R. W. Dean              Director                  November 24, 1998
-----------------------------
          R. W. Dean

      /s/ P. O. Elbert            Director                  November 24, 1998
-----------------------------
          P. O. Elbert

      /s/ W. R. Jackson           Director                  November 30, 1998
-----------------------------
          W. R. Jackson

      /s/ W. R. Jackson, Jr.      Director                  November 30, 1998
-----------------------------
          W. R. Jackson, Jr.

      /s/ W. E. Lewellen          Director                  November 28, 1998
-----------------------------
          W. E. Lewellen

      /s/ A. J. Paddock           Director                  November 30, 1998
-----------------------------
          A. J. Paddock

      /s/ J. W. Robinson          Director                  November 24, 1998
-----------------------------
          J. W. Robinson

      /s/ P. J. Townsend          Director                  December 2, 1998
-----------------------------
          P. J. Townsend
Exhibit Index

  5.1     Opinion of Buchanan Ingersoll Professional Corporation as to the
          legality of the Common Stock issued pursuant to the Plan (filed
          herewith)

 23.1     Consent of Independent Auditors, Ernst & Young LLP (filed herewith)

 23.2     Consent of Buchanan Ingersoll Professional Corporation (contained in
          their opinion filed as Exhibit 5.1 hereto)

 24.1     Powers of Attorney (filed herewith on the signature page)