As filed with the Securities and Exchange Commission on January 4, 1999

                                                    Registration Number 333-____


                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   ----------

                                    FORM S-8

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                                   ----------

                               OMNICOM GROUP INC.
             (Exact name of registrant as specified in its charter)

             New York                                        13-1514814
   (State or other jurisdiction                           (I.R.S. Employer
of incorporation or organization)                      Identification Number)

            437 Madison Avenue
            New York, New York                                  10022
 (Address of Principal Executive Offices)                     (Zip Code)

               OMNICOM GROUP INC. 1998 INCENTIVE COMPENSATION PLAN
                            (Full title of the plan)

                              Barry J. Wagner, Esq.
                          Secretary and General Counsel
                               Omnicom Group Inc.
                               437 Madison Avenue
                            New York, New York 10022
                                 (212) 415-3600
                      (Name, address and telephone number,
                   including area code, of agent for service)

                                   ----------

                                   Copies to:
                              Linda E. Ransom, Esq.
                              Dewey Ballantine LLP
                           1301 Avenue of the Americas
                            New York, New York 10019
                                 (212) 259-6570

                                   ----------

<PAGE>

                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>

=======================================================================================================
       Title of                         Proposed Maximum     Proposed Maximum
    Securities to      Amount to be    Offering Price Per   Aggregate Offering          Amount of
    be Registered       Registered          Share (1)            Price (1)         Registration Fee (1)
-------------------------------------------------------------------------------------------------------
<S>                     <C>                <C>                 <C>                     <C>
Common Stock of
Omnicom Group Inc.,
par value $.50 per
share ................  7,600,000          $57.15625           $434,387,500            $120,759.73
=======================================================================================================
</TABLE>

(1)   Estimated for the sole purpose of computing the registration fee. Pursuant
      to Securities Act Rules 457(c) and (h), the proposed maximum offering
      price per share is calculated as the average of the high and low prices,
      reported by the New York Stock Exchange, Inc., of the common stock of the
      registrant as of December 29, 1998.

<PAGE>

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

      The following documents have been filed by Omnicom Group Inc. (the
"Company") (File No. 1-10551) with the Securities and Exchange Commission (the
"Commission") and are incorporated herein by reference:

      (a)   the Company's Annual Report on Form 10-K for the fiscal year ended
            December 31, 1997;

      (b)   the Company's Quarterly Reports on Form 10-Q for the quarters ended
            March 31, 1998, June 30, 1998 and September 30, 1998;

      (c)   the Company's Current Reports on Form 8-K dated January 20, 1998,
            March 4, 1998 and March 6, 1998; and

      (d)   the description of the Company's Common Stock contained in the
            Registration Statement filed pursuant to Section 12 of the
            Securities Exchange Act of 1934, as amended (the "Exchange Act"),
            and any amendment or report filed for purposes of updating that
            description.

      All documents filed by the Company with the Commission pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act subsequent to the date
of this Registration Statement and 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, shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of filing of such documents. Any statement contained in any
document incorporated or deemed to be incorporated by reference herein shall be
deemed to be modified or superseded for purposes of this Registration Statement
to the extent that a statement contained herein or in any other subsequently
filed document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement. Any such statement so modified or
superseded shall not be deemed, except as modified or superseded, to constitute
a part of this Registration Statement.

      The consolidated financial statements and financial statement schedules of
the Company and its subsidiaries included in the Company's Annual Report on Form
10-K for the fiscal year ended December 31, 1997 have been incorporated herein
by reference in reliance on the reports, also incorporated herein by reference,
of Arthur Andersen LLP, independent certified public accountants, given on their
authority as experts in auditing and accounting.


                                      II-1
<PAGE>

Item 4. Description of Securities.

      Not applicable.

Item 5. Interests of Named Experts and Counsel.

      Not applicable.

Item 6. Indemnification of Directors and Officers.

      The Company's Certificate of Incorporation contains a provision limiting
the liability of directors (except for approving statutorily prohibited
dividends, share repurchases or redemptions, distributions of assets on
dissolution or loans to directors) to acts or omissions in bad faith, involving
intentional misconduct or a knowing violation of the law, or resulting in
personal gain to which the director was not legally entitled. The Company's
By-Laws provide that an officer or director will be indemnified against any
costs or liabilities, including attorneys fees and amounts paid in settlement
with the consent of the Company in connection with any claim, action or
proceeding to the fullest extent permitted by the New York Business Corporation
Law.

      Section 722(a) of the New York Business Corporation Law provides that a
corporation may indemnify any officer or director made, or threatened to be
made, a party to an action other than one by or in the right of the corporation,
including an action by or in the right of any other corporation or other
enterprise which any director or officer of the corporation served in any
capacity at the request of the corporation, because he was a director or officer
of the corporation, or served such other corporation or other enterprise in any
capacity, against judgments, fines, amounts paid in settlement and reasonable
expenses, including attorney's fees actually and necessarily incurred as a
result of such action, or any appeal therein, if such director or officer acted,
in good faith, for a purpose which he reasonably believed to be in, or in the
case of service for any other corporation or other enterprise, not opposed to,
the best interests of the corporation and, in criminal actions, in addition, had
no reasonable cause to believe that his conduct was unlawful.

      Section 722(c) of the New York Business Corporation Law provides that a
corporation may indemnify any officer or director made, or threatened to be
made, a party to an action by or in the right of the corporation by reason of
the fact that he is or was an officer or director of the corporation, or is or
was serving at the request of the corporation as a director or officer of any
other corporation, or other enterprise, against amounts paid in settlement and
reasonable expenses, including attorneys' fees, actually and necessarily
incurred by him in connection with the defense or settlement of such action, or
in connection with an appeal therein, if such director or officer acted, in good
faith, for a purpose which he reasonably believed to be in, or, in the case of
service for another corporation or other enterprise, not opposed to, the best
interests of the corporation. The corporation may not, however, indemnify any
officer or director pursuant to Section 722(c) in respect of (1) a threatened
action, or a pending action which is settled or otherwise disposed of, or (2)
any claim, issue or matter as to which such person shall


                                      II-2
<PAGE>

have been adjudged to be liable to the corporation, unless and only to the
extent that the court in which the action was brought or, if no action was
brought, any court of competent jurisdiction, determines in its discretion, that
the person is fairly and reasonably entitled to indemnity for such portion of
the settlement and expenses as the court deems proper.

      Section 723 of the New York Business Corporation Law provides that an
officer or director who has been successful on the merits or otherwise in the
defense of a civil or criminal action of the character set forth in Section 722
is entitled to indemnification as permitted in such section. Section 724 of the
New York Business Corporation Law permits a court to award the indemnification
required by Section 722.

      The Company has entered into agreements with its directors to indemnify
them for liabilities or costs arising out of any alleged or actual breach of
duty, neglect, errors or omissions while serving as a director. The Company also
maintains and pays premiums for directors' and officers' liability insurance
policies.

Item 7. Exemption from Registration Claimed.

      Not applicable.

Item 8. Exhibits.

  Exhibit Number                    Description
  --------------                    -----------
      5          Opinion and Consent of Dewey Ballantine LLP.

     23.1        Consent of Dewey Ballantine LLP (included in Exhibit 5 hereto).

     23.2        Consent of Arthur Andersen LLP.

     24          Power of Attorney (included on Signature Page).

     99          Omnicom Group Inc. 1998 Incentive Compensation Plan.


Item 9. Undertakings.

      (a) 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:

                  (i) to include any prospectus required by Section 10(a)(3) of
            the Securities Act of 1933;

                  (ii) to reflect in the prospectus any facts or events arising
            after the effective date of the Registration Statement (or the most
            recent post-effective 


                                      II-3
<PAGE>

            amendment thereof) which, individually or in the aggregate,
            represent a fundamental change in the information set forth in the
            Registration Statement; and

                  (iii) to include any material information with respect to the
            plan of distribution not previously disclosed in the Registration
            Statement or any material change to such information in the
            Registration Statement;

provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed with or furnished to the
Commission by the registrant pursuant to Section 13 or Section 15(d) of the
Securities Exchange Act of 1934 that are incorporated by reference in the
Registration Statement.

            (2) That, for the purpose of determining any liability under the
      Securities Act of 1933, 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.

      (b) The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to Section 15(d) of the
Securities Exchange Act of 1934) that is incorporated by reference in this
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered herein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

      (c) Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the registrant 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.


                                      II-4
<PAGE>

                                   SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, as amended,
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 City of New York, State of New York, on January 4, 1999.

                                     OMNICOM GROUP INC.
                                    
                                      By: /s/ John Wren
                                          ------------------------------------
                                          John Wren
                                          Chief Executive Officer and Director
                                    
      Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed by the following persons in the
capacities and on the date indicated. Each person whose signature appears below
does hereby constitute and appoint John Wren and Barry J. Wagner, and each of
them, with full powers of substitution, his or her true and lawful
attorneys-in-fact and agents to do any and all acts and things and to execute
any and all instruments which said attorneys-in-fact and agents may deem
necessary or advisable to enable the registrant to comply with the Securities
Act of 1933, as amended, and any rules, regulations and requirements of the
Securities and Exchange Commission in respect thereof, in connection with the
registration under said Act of shares of Common Stock registered pursuant
hereto, including specifically, but without limitation thereof, power and
authority to sign his or her name, in any and all capacities set forth beneath
his name, to any amendment to this Registration Statement in respect of said
shares and to any documents filed as part of or in connection with said
Registration Statement or amendments; and the undersigned does hereby ratify and
confirm all that said attorneys-in-fact and agents shall do or cause to be done
by virtue hereof.

Date:  January 4, 1999                By: /s/ John Wren
                                          ------------------------------------
                                          John Wren
                                          Chief Executive Officer and Director
                                          (Principal Executive Officer)

Date:  January 4, 1999                By: /s/ Randall Weisenburger
                                          ------------------------------------
                                          Randall Weisenburger
                                          Chief Financial Officer
                                          (Principal Financial Officer)


<PAGE>

Date:  January 4, 1999                By: /s/ Jonathan E. Ramsden
                                          ------------------------------------
                                          Jonathan E. Ramsden
                                          Controller
                                          (Principal Accounting Officer)

Date:  January 4, 1999                By: /s/ Bernard Brochand
                                          ------------------------------------
                                          Bernard Brochand
                                          Director

Date:  January 4, 1999                By: /s/ Robert J. Callander
                                          ------------------------------------
                                          Robert J. Callander
                                          Director

Date:  January 4, 1999                By: /s/ James A. Cannon
                                          ------------------------------------
                                          James A. Cannon
                                          Director

Date:  January 4, 1999                By: /s/ Leonard S. Coleman, Jr.
                                          ------------------------------------
                                          Leonard S. Coleman, Jr.
                                          Director

Date:  January 4, 1999                By: /s/ Bruce Crawford
                                          ------------------------------------
                                          Bruce Crawford
                                          Director

Date:  January 4, 1999                By: /s/ Susan S. Denison
                                          ------------------------------------
                                          Susan S. Denison
                                          Director

Date:  January 4, 1999                By: /s/ John R. Murphy
                                          ------------------------------------
                                          John R. Murphy
                                          Director

Date:  January 4, 1999                By: /s/ John R. Purcell
                                          ------------------------------------
                                          John R. Purcell
                                          Director

<PAGE>

Date:  January 4, 1999                By: /s/ Keith L. Reinhard
                                          ------------------------------------
                                          Keith L. Reinhard
                                          Director

Date:  January 4, 1999                By: /s/ Allen Rosenshine
                                          ------------------------------------
                                          Allen Rosenshine
                                          Director

Date:  January 4, 1999                By: /s/ Gary L. Roubos
                                          ------------------------------------
                                          Gary L. Roubos
                                          Director

Date:  January 4, 1999                By: /s/ Quentin I. Smith, Jr.
                                          ------------------------------------
                                          Quentin I. Smith, Jr.
                                          Director

Date:  January 4, 1999                By: /s/ William G. Tragos
                                          ------------------------------------
                                          William G. Tragos
                                          Director

Date:  January 4, 1999                By: /s/ Egon P. S. Zehnder
                                          ------------------------------------
                                          Egon P. S. Zehnder
                                          Director

<PAGE>

                                INDEX TO EXHIBITS

Exhibit Number                     Description
--------------                     -----------
    5            Opinion and Consent of Dewey Ballantine LLP.

   23.1          Consent of Dewey Ballantine LLP (included in Exhibit 5 hereto).

   23.2          Consent of Arthur Andersen LLP.

   24            Power of Attorney (included on Signature Page).

   99            Omnicom Group Inc. 1998 Incentive Compensation Plan.
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 21846}]
{"company-data": {"conformed-name": "OMNICOM GROUP INC", "cik": "0000029989", "assigned-sic": "7311", "irs-number": "131514814", "state-of-incorporation": "NY", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-70091", "film-number": "99500323"}, "business-address": {"street1": "437 MADISON AVE", "city": "NEW YORK", "state": "NY", "zip": "10022", "phone": "2124153700"}, "mail-address": {"street1": "437 MADISON AVE", "city": "NEW YORK", "state": "NY", "zip": "10022"}, "former-company": [{"former-conformed-name": "DOYLE DANE BERNBACH GROUP INC", "date-changed": "19861117"}, {"former-conformed-name": "DOYLE DANE BERNBACH INTERNATIONAL INC", "date-changed": "19850604"}, {"former-conformed-name": "DOYLE DANE BERNBACH INC", "date-changed": "19781226"}]}
As filed with the Securities and Exchange Commission on January 4, 1999

                                                    Registration Number 333-____

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   ----------

                                    FORM S-8

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                                   ----------

                               OMNICOM GROUP INC.
             (Exact name of registrant as specified in its charter)

             New York                                        13-1514814
   (State or other jurisdiction                           (I.R.S. Employer
of incorporation or organization)                      Identification Number)

            437 Madison Avenue
            New York, New York                                  10022
 (Address of Principal Executive Offices)                     (Zip Code)

               OMNICOM GROUP INC. 1998 INCENTIVE COMPENSATION PLAN
                            (Full title of the plan)

                              Barry J. Wagner, Esq.
                          Secretary and General Counsel
                               Omnicom Group Inc.
                               437 Madison Avenue
                            New York, New York 10022
                                 (212) 415-3600
                      (Name, address and telephone number,
                   including area code, of agent for service)

                                   ----------

                                   Copies to:
                              Linda E. Ransom, Esq.
                              Dewey Ballantine LLP
                           1301 Avenue of the Americas
                            New York, New York 10019
                                 (212) 259-6570

                                   ----------
CALCULATION OF REGISTRATION FEE
=======================================================================================================
       Title of                         Proposed Maximum     Proposed Maximum
    Securities to      Amount to be    Offering Price Per   Aggregate Offering          Amount of
    be Registered       Registered          Share (1)            Price (1)         Registration Fee (1)
-------------------------------------------------------------------------------------------------------
Common Stock of
Omnicom Group Inc.,
par value $.50 per
share ................  7,600,000          $57.15625           $434,387,500            $120,759.73
=======================================================================================================
(1)   Estimated for the sole purpose of computing the registration fee. Pursuant
      to Securities Act Rules 457(c) and (h), the proposed maximum offering
      price per share is calculated as the average of the high and low prices,
      reported by the New York Stock Exchange, Inc., of the common stock of the
      registrant as of December 29, 1998.
PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

      The following documents have been filed by Omnicom Group Inc. (the
"Company") (File No. 1-10551) with the Securities and Exchange Commission (the
"Commission") and are incorporated herein by reference:

      (a)   the Company's Annual Report on Form 10-K for the fiscal year ended
            December 31, 1997;

      (b)   the Company's Quarterly Reports on Form 10-Q for the quarters ended
            March 31, 1998, June 30, 1998 and September 30, 1998;

      (c)   the Company's Current Reports on Form 8-K dated January 20, 1998,
            March 4, 1998 and March 6, 1998; and

      (d)   the description of the Company's Common Stock contained in the
            Registration Statement filed pursuant to Section 12 of the
            Securities Exchange Act of 1934, as amended (the "Exchange Act"),
            and any amendment or report filed for purposes of updating that
            description.

      All documents filed by the Company with the Commission pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act subsequent to the date
of this Registration Statement and 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, shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of filing of such documents. Any statement contained in any
document incorporated or deemed to be incorporated by reference herein shall be
deemed to be modified or superseded for purposes of this Registration Statement
to the extent that a statement contained herein or in any other subsequently
filed document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement. Any such statement so modified or
superseded shall not be deemed, except as modified or superseded, to constitute
a part of this Registration Statement.

      The consolidated financial statements and financial statement schedules of
the Company and its subsidiaries included in the Company's Annual Report on Form
10-K for the fiscal year ended December 31, 1997 have been incorporated herein
by reference in reliance on the reports, also incorporated herein by reference,
of Arthur Andersen LLP, independent certified public accountants, given on their
authority as experts in auditing and accounting.

                                      II-1
Item 4. Description of Securities.

      Not applicable.

Item 5. Interests of Named Experts and Counsel.

      Not applicable.

Item 6. Indemnification of Directors and Officers.

      The Company's Certificate of Incorporation contains a provision limiting
the liability of directors (except for approving statutorily prohibited
dividends, share repurchases or redemptions, distributions of assets on
dissolution or loans to directors) to acts or omissions in bad faith, involving
intentional misconduct or a knowing violation of the law, or resulting in
personal gain to which the director was not legally entitled. The Company's
By-Laws provide that an officer or director will be indemnified against any
costs or liabilities, including attorneys fees and amounts paid in settlement
with the consent of the Company in connection with any claim, action or
proceeding to the fullest extent permitted by the New York Business Corporation
Law.

      Section 722(a) of the New York Business Corporation Law provides that a
corporation may indemnify any officer or director made, or threatened to be
made, a party to an action other than one by or in the right of the corporation,
including an action by or in the right of any other corporation or other
enterprise which any director or officer of the corporation served in any
capacity at the request of the corporation, because he was a director or officer
of the corporation, or served such other corporation or other enterprise in any
capacity, against judgments, fines, amounts paid in settlement and reasonable
expenses, including attorney's fees actually and necessarily incurred as a
result of such action, or any appeal therein, if such director or officer acted,
in good faith, for a purpose which he reasonably believed to be in, or in the
case of service for any other corporation or other enterprise, not opposed to,
the best interests of the corporation and, in criminal actions, in addition, had
no reasonable cause to believe that his conduct was unlawful.

      Section 722(c) of the New York Business Corporation Law provides that a
corporation may indemnify any officer or director made, or threatened to be
made, a party to an action by or in the right of the corporation by reason of
the fact that he is or was an officer or director of the corporation, or is or
was serving at the request of the corporation as a director or officer of any
other corporation, or other enterprise, against amounts paid in settlement and
reasonable expenses, including attorneys' fees, actually and necessarily
incurred by him in connection with the defense or settlement of such action, or
in connection with an appeal therein, if such director or officer acted, in good
faith, for a purpose which he reasonably believed to be in, or, in the case of
service for another corporation or other enterprise, not opposed to, the best
interests of the corporation. The corporation may not, however, indemnify any
officer or director pursuant to Section 722(c) in respect of (1) a threatened
action, or a pending action which is settled or otherwise disposed of, or (2)
any claim, issue or matter as to which such person shall

                                      II-2
have been adjudged to be liable to the corporation, unless and only to the
extent that the court in which the action was brought or, if no action was
brought, any court of competent jurisdiction, determines in its discretion, that
the person is fairly and reasonably entitled to indemnity for such portion of
the settlement and expenses as the court deems proper.

      Section 723 of the New York Business Corporation Law provides that an
officer or director who has been successful on the merits or otherwise in the
defense of a civil or criminal action of the character set forth in Section 722
is entitled to indemnification as permitted in such section. Section 724 of the
New York Business Corporation Law permits a court to award the indemnification
required by Section 722.

      The Company has entered into agreements with its directors to indemnify
them for liabilities or costs arising out of any alleged or actual breach of
duty, neglect, errors or omissions while serving as a director. The Company also
maintains and pays premiums for directors' and officers' liability insurance
policies.

Item 7. Exemption from Registration Claimed.

      Not applicable.

Item 8. Exhibits.

  Exhibit Number                    Description
  --------------                    -----------
      5          Opinion and Consent of Dewey Ballantine LLP.

     23.1        Consent of Dewey Ballantine LLP (included in Exhibit 5 hereto).

     23.2        Consent of Arthur Andersen LLP.

     24          Power of Attorney (included on Signature Page).

     99          Omnicom Group Inc. 1998 Incentive Compensation Plan.

Item 9. Undertakings.

      (a) 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:

                  (i) to include any prospectus required by Section 10(a)(3) of
            the Securities Act of 1933;

                  (ii) to reflect in the prospectus any facts or events arising
            after the effective date of the Registration Statement (or the most
            recent post-effective 

                                      II-3
amendment thereof) which, individually or in the aggregate,
            represent a fundamental change in the information set forth in the
            Registration Statement; and

                  (iii) to include any material information with respect to the
            plan of distribution not previously disclosed in the Registration
            Statement or any material change to such information in the
            Registration Statement;

provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed with or furnished to the
Commission by the registrant pursuant to Section 13 or Section 15(d) of the
Securities Exchange Act of 1934 that are incorporated by reference in the
Registration Statement.

            (2) That, for the purpose of determining any liability under the
      Securities Act of 1933, 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.

      (b) The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to Section 15(d) of the
Securities Exchange Act of 1934) that is incorporated by reference in this
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered herein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

      (c) Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the registrant 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.

                                      II-4
SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, as amended,
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 City of New York, State of New York, on January 4, 1999.

                                     OMNICOM GROUP INC.
                                    
                                      By: /s/ John Wren
                                          ------------------------------------
                                          John Wren
                                          Chief Executive Officer and Director
                                    
      Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed by the following persons in the
capacities and on the date indicated. Each person whose signature appears below
does hereby constitute and appoint John Wren and Barry J. Wagner, and each of
them, with full powers of substitution, his or her true and lawful
attorneys-in-fact and agents to do any and all acts and things and to execute
any and all instruments which said attorneys-in-fact and agents may deem
necessary or advisable to enable the registrant to comply with the Securities
Act of 1933, as amended, and any rules, regulations and requirements of the
Securities and Exchange Commission in respect thereof, in connection with the
registration under said Act of shares of Common Stock registered pursuant
hereto, including specifically, but without limitation thereof, power and
authority to sign his or her name, in any and all capacities set forth beneath
his name, to any amendment to this Registration Statement in respect of said
shares and to any documents filed as part of or in connection with said
Registration Statement or amendments; and the undersigned does hereby ratify and
confirm all that said attorneys-in-fact and agents shall do or cause to be done
by virtue hereof.

Date:  January 4, 1999                By: /s/ John Wren
                                          ------------------------------------
                                          John Wren
                                          Chief Executive Officer and Director
                                          (Principal Executive Officer)

Date:  January 4, 1999                By: /s/ Randall Weisenburger
                                          ------------------------------------
                                          Randall Weisenburger
                                          Chief Financial Officer
                                          (Principal Financial Officer)
Date:  January 4, 1999                By: /s/ Jonathan E. Ramsden
                                          ------------------------------------
                                          Jonathan E. Ramsden
                                          Controller
                                          (Principal Accounting Officer)

Date:  January 4, 1999                By: /s/ Bernard Brochand
                                          ------------------------------------
                                          Bernard Brochand
                                          Director

Date:  January 4, 1999                By: /s/ Robert J. Callander
                                          ------------------------------------
                                          Robert J. Callander
                                          Director

Date:  January 4, 1999                By: /s/ James A. Cannon
                                          ------------------------------------
                                          James A. Cannon
                                          Director

Date:  January 4, 1999                By: /s/ Leonard S. Coleman, Jr.
                                          ------------------------------------
                                          Leonard S. Coleman, Jr.
                                          Director

Date:  January 4, 1999                By: /s/ Bruce Crawford
                                          ------------------------------------
                                          Bruce Crawford
                                          Director

Date:  January 4, 1999                By: /s/ Susan S. Denison
                                          ------------------------------------
                                          Susan S. Denison
                                          Director

Date:  January 4, 1999                By: /s/ John R. Murphy
                                          ------------------------------------
                                          John R. Murphy
                                          Director

Date:  January 4, 1999                By: /s/ John R. Purcell
                                          ------------------------------------
                                          John R. Purcell
                                          Director
Date:  January 4, 1999                By: /s/ Keith L. Reinhard
                                          ------------------------------------
                                          Keith L. Reinhard
                                          Director

Date:  January 4, 1999                By: /s/ Allen Rosenshine
                                          ------------------------------------
                                          Allen Rosenshine
                                          Director

Date:  January 4, 1999                By: /s/ Gary L. Roubos
                                          ------------------------------------
                                          Gary L. Roubos
                                          Director

Date:  January 4, 1999                By: /s/ Quentin I. Smith, Jr.
                                          ------------------------------------
                                          Quentin I. Smith, Jr.
                                          Director

Date:  January 4, 1999                By: /s/ William G. Tragos
                                          ------------------------------------
                                          William G. Tragos
                                          Director

Date:  January 4, 1999                By: /s/ Egon P. S. Zehnder
                                          ------------------------------------
                                          Egon P. S. Zehnder
                                          Director
INDEX TO EXHIBITS

Exhibit Number                     Description
--------------                     -----------
    5            Opinion and Consent of Dewey Ballantine LLP.

   23.1          Consent of Dewey Ballantine LLP (included in Exhibit 5 hereto).

   23.2          Consent of Arthur Andersen LLP.

   24            Power of Attorney (included on Signature Page).

   99            Omnicom Group Inc. 1998 Incentive Compensation Plan.