<PAGE>
                                                       REGISTRATION NO. 33-
 
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
 
                                    FORM S-8
 
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
 
                            ------------------------
 
                         ROBERT HALF INTERNATIONAL INC.
 
             (Exact name of registrant as specified in its charter)
 
                DELAWARE                                94-1648752
    (State or other jurisdiction of        (I.R.S. Employer Identification No.)
     incorporation or organization)
 
    2884 SAND HILL ROAD, SUITE 200, MENLO PARK, CALIFORNIA            94025
           (Address of Principal Executive Offices)                (Zip Code)
 
                 1991 RESTRICTED STOCK PLAN FOR FIELD EMPLOYEES
 
                            (Full title of the plan)
 
                                  STEVEN KAREL
                       VICE PRESIDENT AND GENERAL COUNSEL
                         ROBERT HALF INTERNATIONAL INC.
                         2884 SAND HILL ROAD, SUITE 200
                          MENLO PARK, CALIFORNIA 94025
 
                    (Name and address of agent for service)
 
                                 (415) 234-6000
 
                    (Telephone number of agent for service)
 
                            ------------------------
 
                        CALCULATION OF REGISTRATION FEE
 
<TABLE>
<CAPTION>
-------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------
                                                   PROPOSED         PROPOSED
                                                    MAXIMUM          MAXIMUM         AMOUNT OF
  TITLE OF SECURITIES TO BE       AMOUNT TO     OFFERING PRICE      AGGREGATE      REGISTRATION
         REGISTERED             BE REGISTERED      PER UNIT      OFFERING PRICE         FEE
-------------------------------------------------------------------------------------------------
<S>                            <C>              <C>              <C>              <C>
 
Common Stock.................      200,000         $33.0625        $6,612,500        $2,003.78
-------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------
</TABLE>
 
(a) Determined in accordance with Rule 457(h) under the Securities Act of 1933,
    based upon the high and low sales prices of the registrant's Common Stock on
    the New York Stock Exchange on December 17, 1996.
 
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>
                                     PART I
 
    The information required by the Note to Part I of Form S-8 to be sent or
given to employees as specified by Rule 428(b)(1) has not been included with
this filing in accordance with such Note.
<PAGE>
                                    PART II
 
ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.
 
    The following documents are incorporated by reference in this Registration
Statement:
 
    (a) The Company's latest Annual Report on Form 10-K;
 
    (b) All other reports filed by the Company pursuant to Section 13(a) or
15(d) of the Securities Exchange Act of 1934, as amended, (the "Exchange Act")
since the end of the fiscal year covered by the Annual Report on Form 10-K
referred to in (a) above;
 
    (c) The description of the Company's Common Stock contained in a
registration statement filed under the Exchange Act, including any amendment or
report filed for the purpose of updating such description.
 
    All documents subsequently filed by the Company pursuant to Sections 13(a),
13(c), 14 and 15(d) of the Exchange Act shall be deemed to be incorporated by
reference herein and to be a part hereof from the date of filing (except that no
documents shall be deemed to be incorporated by reference if filed after the
filing of a post-effective amendment which deregisters securities then remaining
unsold).
 
ITEM 4.  DESCRIPTION OF SECURITIES.
 
    Not applicable.
 
ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.
 
    Not applicable.
 
ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.
 
    Section 145 of the Delaware General Corporation Law authorizes a corporation
to indemnify its directors and officers under the terms and circumstances
described therein. The Restated Certificate of Incorporation of the Company
provides that each director, officer and employee of the Company shall be
indemnified and held harmless by the Company to the fullest extent authorized by
the Delaware General Corporation Law against all expenses, liabilities and
losses incurred or suffered by such individual in his capacity as director,
officer or employee. The right to indemnification contained in the Restated
Certificate of Incorporation includes the right, subject to the conditions
contained therein, to be reimbursed for expenses in advance of the final
disposition of any action, suit or proceeding. The Registrant has entered into
Indemnification Agreements with each of its directors and certain executive
officers (the form of which Indemnification Agreements was approved by the
Company's stockholders in May 1989) that provide, among other things, for (a)
indemnification, under the terms and circumstances described in the
Indemnification Agreements, to the fullest extent not prohibited by applicable
law, against any and all expenses and liabilities resulting from service with
the Company and (b) advancement to the individual of expenses reasonably
incurred in connection with any threatened or actual action, suit or proceeding
in which such individual is involved by reason of having been a director,
officer, or employee. The Company has insured its directors and officers against
certain liabilities and has insurance against certain payments which it may be
obligated to make to such persons pursuant to the indemnification provisions of
its Restated Certificate of Incorporation or pursuant to the Indemnification
Agreements described above.
 
ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.
 
    Not applicable.
 
ITEM 8.  EXHIBITS.
 
<TABLE>
<CAPTION>
  NUMBER     EXHIBIT
-----------  ------------------------------------------------------------------------------------
<S>          <C>
      23.1   Consent of Arthur Andersen LLP
</TABLE>
 
<PAGE>
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 (unless the information required to be included in
       a post-effective amendment by this paragraph is contained in periodic
       reports filed by the registrant pursuant to Section 13 or Section 15(d)
       of the Securities Exchange Act of 1934 that are incorporated by reference
       in this registration statement);
 
            (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 amendment thereof) which, individually or in the
       aggregate, represent a fundamental change in the information set forth in
       the registration statement (unless the information required to be
       included in a post-effective amendment by this paragraph is contained in
       periodic reports filed by the registrant pursuant to Section 13 or
       Section 15(d) of the Securities Exchange Act of 1934 that are
       incorporated by reference in this registration statement);
 
           (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.
 
        (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 that is incorporated by reference in the
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.
 
    (h) 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 provisions described herein, 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
Securities Act of 1933 and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than 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 of whether such
indemnification by it is against public policy as expressed in the Securities
Act of 1933 and will be governed by the final adjudication of such issue.
<PAGE>
                                   SIGNATURES
 
    Pursuant to the requirements of the Securities Act of 1933, 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 Menlo Park, State of California, on December 19,
1996.
 
                              ROBERT HALF INTERNATIONAL INC.
                              (Registrant)
 
                              By:             /s/ M. KEITH WADDELL
                                   -----------------------------------------
                                                M. Keith Waddell
                                     SENIOR VICE PRESIDENT, CHIEF FINANCIAL
                                   OFFICER AND TREASURER (PRINCIPAL FINANCIAL
                                                    OFFICER)
 
    KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints Harold M. Messmer, Jr. and M. Keith Waddell,
jointly and severally, his attorney-in-fact, each with full power of
substitution, for him in any and all capacities, to sign any amendments to this
registration statement, and to file the same, with exhibits thereto and other
documents in connection therewith, with the Securities and Exchange Commission,
hereby ratifying and confirming all that each of said attorneys-in-fact, or his
substitute or substitutes, may do or cause to be done by virtue hereof.
 
    Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed below by the following persons on behalf
of the Company and in the capacities and on the dates indicated.
 
<TABLE>
<C>                                        <S>                              <C>
       /s/ HAROLD M. MESSMER, JR.          Chairman and Chief Executive
  ------------------------------------       Officer, and a Director        Date: December 19, 1996
         Harold M. Messmer, Jr.              (Principal Executive
                                             Officer)
 
       /s/ ANDREW S. BERWICK, JR.
  ------------------------------------     Director                         Date: December 19, 1996
         Andrew S. Berwick, Jr.
 
         /s/ FREDERICK P. FURTH
  ------------------------------------     Director                         Date: December 19, 1996
           Frederick P. Furth
 
         /s/ EDWARD W. GIBBONS
  ------------------------------------     Director                         Date: December 19, 1996
           Edward W. Gibbons
 
  ------------------------------------     Director                         Date:            , 1996
          Frederick A. Richman
 
           /s/ THOMAS J. RYAN
  ------------------------------------     Director                         Date: December 19, 1996
             Thomas J. Ryan
 
         /s/ J. STEPHEN SCHAUB
  ------------------------------------     Director                         Date: December 19, 1996
           J. Stephen Schaub
 
          /s/ M. KEITH WADDELL             Senior Vice President, Chief
  ------------------------------------       Financial Officer and          Date: December 19, 1996
            M. Keith Waddell                 Treasurer (Principal
                                             Financial Officer)
 
        /s/ BARBARA J. FORSBERG            Vice President and Controller
  ------------------------------------       (Principal Accounting          Date: December 19, 1996
          Barbara J. Forsberg                Officer)
</TABLE>
<PAGE>
                               INDEX TO EXHIBITS
 
<TABLE>
<CAPTION>
                                                                                                            SEQUENTIALLY
  NUMBER     EXHIBIT                                                                                        NUMBERED PAGE
-----------  -------------------------------------------------------------------------------------------  -----------------
<S>          <C>                                                                                          <C>
      23.1   Consent of Arthur Andersen LLP.............................................................
</TABLE>
[{"type": "S-8", "sequence": "1", "description": "S-8", "secsgml_size_bytes": 14990}]
{"company-data": {"conformed-name": "HALF ROBERT INTERNATIONAL INC /DE/", "cik": "0000315213", "assigned-sic": "7363", "irs-number": "941648752", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-18283", "film-number": "96683428"}, "business-address": {"street1": "2884 SAND HILL ROAD", "street2": "STE 200", "city": "MENLO PARK", "state": "CA", "zip": "94025", "phone": "4158549700"}, "mail-address": {"street1": "2884 SAND HILL ROAD", "street2": "STE 200", "city": "MENLO PARK", "state": "CA", "zip": "94025"}, "former-company": [{"former-conformed-name": "BOOTHE FINANCIAL CORP /DE/", "date-changed": "19870721"}, {"former-conformed-name": "BOOTHE INTERIM CORP", "date-changed": "19600201"}]}
REGISTRATION NO. 33-
 
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
 
                                    FORM S-8
 
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
 
                            ------------------------
 
                         ROBERT HALF INTERNATIONAL INC.
 
             (Exact name of registrant as specified in its charter)
 
                DELAWARE                                94-1648752
    (State or other jurisdiction of        (I.R.S. Employer Identification No.)
     incorporation or organization)
 
    2884 SAND HILL ROAD, SUITE 200, MENLO PARK, CALIFORNIA            94025
           (Address of Principal Executive Offices)                (Zip Code)
 
                 1991 RESTRICTED STOCK PLAN FOR FIELD EMPLOYEES
 
                            (Full title of the plan)
 
                                  STEVEN KAREL
                       VICE PRESIDENT AND GENERAL COUNSEL
                         ROBERT HALF INTERNATIONAL INC.
                         2884 SAND HILL ROAD, SUITE 200
                          MENLO PARK, CALIFORNIA 94025
 
                    (Name and address of agent for service)
 
                                 (415) 234-6000
 
                    (Telephone number of agent for service)
 
                            ------------------------
 
                        CALCULATION OF REGISTRATION FEE
-------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------
                                                   PROPOSED         PROPOSED
                                                    MAXIMUM          MAXIMUM         AMOUNT OF
  TITLE OF SECURITIES TO BE       AMOUNT TO     OFFERING PRICE      AGGREGATE      REGISTRATION
         REGISTERED             BE REGISTERED      PER UNIT      OFFERING PRICE         FEE
-------------------------------------------------------------------------------------------------
Common Stock.................      200,000         $33.0625        $6,612,500        $2,003.78
-------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------
(a) Determined in accordance with Rule 457(h) under the Securities Act of 1933,
    based upon the high and low sales prices of the registrant's Common Stock on
    the New York Stock Exchange on December 17, 1996.
 
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
PART I
 
    The information required by the Note to Part I of Form S-8 to be sent or
given to employees as specified by Rule 428(b)(1) has not been included with
this filing in accordance with such Note.
PART II
 
ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.
 
    The following documents are incorporated by reference in this Registration
Statement:
 
    (a) The Company's latest Annual Report on Form 10-K;
 
    (b) All other reports filed by the Company pursuant to Section 13(a) or
15(d) of the Securities Exchange Act of 1934, as amended, (the "Exchange Act")
since the end of the fiscal year covered by the Annual Report on Form 10-K
referred to in (a) above;
 
    (c) The description of the Company's Common Stock contained in a
registration statement filed under the Exchange Act, including any amendment or
report filed for the purpose of updating such description.
 
    All documents subsequently filed by the Company pursuant to Sections 13(a),
13(c), 14 and 15(d) of the Exchange Act shall be deemed to be incorporated by
reference herein and to be a part hereof from the date of filing (except that no
documents shall be deemed to be incorporated by reference if filed after the
filing of a post-effective amendment which deregisters securities then remaining
unsold).
 
ITEM 4.  DESCRIPTION OF SECURITIES.
 
    Not applicable.
 
ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.
 
    Not applicable.
 
ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.
 
    Section 145 of the Delaware General Corporation Law authorizes a corporation
to indemnify its directors and officers under the terms and circumstances
described therein. The Restated Certificate of Incorporation of the Company
provides that each director, officer and employee of the Company shall be
indemnified and held harmless by the Company to the fullest extent authorized by
the Delaware General Corporation Law against all expenses, liabilities and
losses incurred or suffered by such individual in his capacity as director,
officer or employee. The right to indemnification contained in the Restated
Certificate of Incorporation includes the right, subject to the conditions
contained therein, to be reimbursed for expenses in advance of the final
disposition of any action, suit or proceeding. The Registrant has entered into
Indemnification Agreements with each of its directors and certain executive
officers (the form of which Indemnification Agreements was approved by the
Company's stockholders in May 1989) that provide, among other things, for (a)
indemnification, under the terms and circumstances described in the
Indemnification Agreements, to the fullest extent not prohibited by applicable
law, against any and all expenses and liabilities resulting from service with
the Company and (b) advancement to the individual of expenses reasonably
incurred in connection with any threatened or actual action, suit or proceeding
in which such individual is involved by reason of having been a director,
officer, or employee. The Company has insured its directors and officers against
certain liabilities and has insurance against certain payments which it may be
obligated to make to such persons pursuant to the indemnification provisions of
its Restated Certificate of Incorporation or pursuant to the Indemnification
Agreements described above.
 
ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.
 
    Not applicable.
 
ITEM 8.  EXHIBITS.
NUMBER     EXHIBIT
-----------  ------------------------------------------------------------------------------------
23.1   Consent of Arthur Andersen LLP
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 (unless the information required to be included in
       a post-effective amendment by this paragraph is contained in periodic
       reports filed by the registrant pursuant to Section 13 or Section 15(d)
       of the Securities Exchange Act of 1934 that are incorporated by reference
       in this registration statement);
 
            (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 amendment thereof) which, individually or in the
       aggregate, represent a fundamental change in the information set forth in
       the registration statement (unless the information required to be
       included in a post-effective amendment by this paragraph is contained in
       periodic reports filed by the registrant pursuant to Section 13 or
       Section 15(d) of the Securities Exchange Act of 1934 that are
       incorporated by reference in this registration statement);
 
           (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.
 
        (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 that is incorporated by reference in the
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.
 
    (h) 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 provisions described herein, 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
Securities Act of 1933 and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than 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 of whether such
indemnification by it is against public policy as expressed in the Securities
Act of 1933 and will be governed by the final adjudication of such issue.
SIGNATURES
 
    Pursuant to the requirements of the Securities Act of 1933, 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 Menlo Park, State of California, on December 19,
1996.
 
                              ROBERT HALF INTERNATIONAL INC.
                              (Registrant)
 
                              By:             /s/ M. KEITH WADDELL
                                   -----------------------------------------
                                                M. Keith Waddell
                                     SENIOR VICE PRESIDENT, CHIEF FINANCIAL
                                   OFFICER AND TREASURER (PRINCIPAL FINANCIAL
                                                    OFFICER)
 
    KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints Harold M. Messmer, Jr. and M. Keith Waddell,
jointly and severally, his attorney-in-fact, each with full power of
substitution, for him in any and all capacities, to sign any amendments to this
registration statement, and to file the same, with exhibits thereto and other
documents in connection therewith, with the Securities and Exchange Commission,
hereby ratifying and confirming all that each of said attorneys-in-fact, or his
substitute or substitutes, may do or cause to be done by virtue hereof.
 
    Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed below by the following persons on behalf
of the Company and in the capacities and on the dates indicated.
/s/ HAROLD M. MESSMER, JR.          Chairman and Chief Executive
  ------------------------------------       Officer, and a Director        Date: December 19, 1996
         Harold M. Messmer, Jr.              (Principal Executive
                                             Officer)
 
       /s/ ANDREW S. BERWICK, JR.
  ------------------------------------     Director                         Date: December 19, 1996
         Andrew S. Berwick, Jr.
 
         /s/ FREDERICK P. FURTH
  ------------------------------------     Director                         Date: December 19, 1996
           Frederick P. Furth
 
         /s/ EDWARD W. GIBBONS
  ------------------------------------     Director                         Date: December 19, 1996
           Edward W. Gibbons
 
  ------------------------------------     Director                         Date:            , 1996
          Frederick A. Richman
 
           /s/ THOMAS J. RYAN
  ------------------------------------     Director                         Date: December 19, 1996
             Thomas J. Ryan
 
         /s/ J. STEPHEN SCHAUB
  ------------------------------------     Director                         Date: December 19, 1996
           J. Stephen Schaub
 
          /s/ M. KEITH WADDELL             Senior Vice President, Chief
  ------------------------------------       Financial Officer and          Date: December 19, 1996
            M. Keith Waddell                 Treasurer (Principal
                                             Financial Officer)
 
        /s/ BARBARA J. FORSBERG            Vice President and Controller
  ------------------------------------       (Principal Accounting          Date: December 19, 1996
          Barbara J. Forsberg                Officer)
INDEX TO EXHIBITS
SEQUENTIALLY
  NUMBER     EXHIBIT                                                                                        NUMBERED PAGE
-----------  -------------------------------------------------------------------------------------------  -----------------
23.1   Consent of Arthur Andersen LLP.............................................................