<PAGE>   1

     As filed with the Securities and Exchange Commission on April 26, 1999

                                                   Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

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

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

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

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

                 Delaware                                      04-3099750
      (State or other jurisdiction of                       (I.R.S. Employer
      incorporation or organization)                       Identification No.)

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

               P.O. Box 10212
             56 Top Gallant Road
            Stamford, Connecticut                               06904-2212
  (Address of  Principal Executive Offices)                     (Zip Code)

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

                   Gartner Group, Inc. 1991 Stock Option Plan
                            (Full title of the plan)

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

                               Michael D. Fleisher
              Chief Financial Officer and Executive Vice President-
                           Finance and Administration
                               Gartner Group, Inc.
                               56 Top Gallant Road
                             Stamford, CT 06904-2212
                     (Name and address of agent for service)

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

                                 (203) 964-0096
          (Telephone number, including area code, of agent for service)

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

                                    Copy to:

                            Michael J. Palmieri, Esq.
                              Shipman & Goodwin LLP
                               One Landmark Square
                               Stamford, CT 06901
                                 (203) 324-8100

<TABLE>
<CAPTION>
                              CALCULATION OF REGISTRATION FEE
==============================================================================================
                                                   Proposed        Proposed
                                                    Maximum         Maximum
     Title of Each Class           Amount          Offering        Aggregate     Amount of
     of Securities to be           to be           Price per       Offering     Registration
          Registered             Registered          Share         Price (1)        Fee
----------------------------------------------------------------------------------------------
<S>                           <C>                   <C>          <C>               <C>    
Common Stock, Class A, par    3,110,914 shares      $21.86       $ 68,003,942      $18,906
value $0.0005 (currently
outstanding options) (1)
----------------------------------------------------------------------------------------------
Common Stock, Class A, par      100,000 shares      $19.3125     $  1,931,250      $   537
value $0.0005 (allocated
shares of restricted stock)
(2)
----------------------------------------------------------------------------------------------
Common Stock, Class A, par    6,789,086 shares      $19.3125     $131,114,223      $36,450
value $0.0005 (shares
available for future
issuance) (2)
----------------------------------------------------------------------------------------------
</TABLE>

<PAGE>   2

<TABLE>
----------------------------------------------------------------------------------------------
<S>                                                                                <C>    
  Total                                                                            $55,893
----------------------------------------------------------------------------------------------
</TABLE>

(1)   In accordance with Rule 457(h), the computation is based on the weighted
      average exercise price per share of $21.86 as to 3,110,914 outstanding but
      unexercised options to purchase Common Stock under the 1991 Stock Option
      Plan.
(2)   In accordance with Rule 457(h), the Proposed Maximum Offering Price per
      Share as to the 100,000 shares of restricted stock to be issued under the
      1991 Stock Option Plan and the remaining 6,789,086 shares of Common Stock
      authorized for issuance pursuant to the 1991 Stock Option Plan has been
      estimated in accordance with Rule 457(c) under the Securities Act of 1933,
      solely for the purpose of calculating the registration fee. The
      computation is based on the average of the high and low price of the
      Common Stock as reported on the New York Stock Exchange on April 21, 1999.
--------------------------------------------------------------------------------
 Pursuant to Rule 429 under the Securities Act of 1933, the prospectus relating
 to the securities registered under this Registration Statement also relates to
                      Registration Statement No. 33-85926.
================================================================================
<PAGE>   3

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

      The information statement being delivered by Gartner Group, Inc. (the
"Company") to participants in the Company's 1991 Stock Option Plan (the "Plan"),
as required by Rule 428 under the Securities Act of 1933, as amended (the
"Securities Act"), has been prepared in accordance with the requirements of Form
S-8 and relates to shares of common stock, par value $0.0005 per share, (the
"Shares") issued or to be issued pursuant to the Plan. The information with
respect to the Plan required in the Section 10(a) prospectus is included in
documents being maintained and delivered by the Company as required by Rule 428
under the Securities Act. The Company shall provide to participants a written
statement advising them of the availability without charge, upon written or oral
request, of documents incorporated by reference herein, as is required by Item 2
of Part I of Form S-8.
<PAGE>   4

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

      The following documents, previously filed with the Commission, are hereby
incorporated by reference in this registration statement:

      (a) The Company's Annual Report on Form 10-K for the year ended September
30, 1998;

      (b) The Company's Quarterly Report on Form 10-Q for the quarter ended
December 31, 1998; and

      (c) The description of the Shares contained in the Registration Statement
on Form 8-A filed on August 24, 1998, filed pursuant to Section 12(b) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), including any
amendment or report filed for the purpose of updating such description.

      In addition, all documents subsequently filed by the Company pursuant to
Section 13(a), 13(c), 14 or 15(d) of the Exchange Act on or after the date of
this Registration Statement and prior to the filing of a post-effective
amendment which indicates that all securities offered hereby 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 a part hereof
from the date of filing of such documents. Any statement contained in a document
incorporated or deemed to be incorporated by reference in this registration
statement 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 so modified or superseded,
to constitute a part of this registration statement.

Item 4. Description of Securities.

      This item is not applicable.

Item 5. Interests of Named Experts and Counsel.

      This item is not applicable.

Item 6. Indemnification of Directors and Officers.
<PAGE>   5

      Section 145 of the Delaware General Corporation Law ("Delaware Law")
provides that a corporation may indemnify a director, officer, employee or agent
made a party to an action by reason of the fact that he was a director, officer,
employee or agent of the corporation, or was serving at the request of the
corporation, against expenses actually and reasonably incurred, including
attorneys' fees, in connection with such action, if he acted in good faith and
in a manner he reasonably believed to be in, or not opposed to, the best
interests of the corporation and, with respect to any criminal action, had no
reasonable cause to believe his conduct was unlawful.

      The Company's Certificate of Incorporation limits, to the maximum extent
permitted by Delaware Law, the personal liability of a director to the Company
or its shareholders for monetary damages for breach of fiduciary duty as a
director. The Company's By-laws provide that the Company shall indemnify its
officers and directors to the fullest extent permitted by Delaware Law against
all expense, liability and loss, including attorneys' fees, actually and
reasonably incurred and may purchase and maintain insurance against any
liability asserted and incurred by reason of serving as such, whether or not the
Company has the power to indemnify against such liability. The Company has
entered into indemnification agreements with its officers and directors
containing provisions which are in some respects broader than the specific
indemnification provisions contained in Delaware Law and which require that, to
the extent the Company maintains liability insurance applicable to officers or
directors, each officer and director shall be covered by such policies to the
same extent as are accorded the most favorably insured of the Company's officers
or directors, as the case may be.

      Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers or persons controlling the Company
pursuant to the foregoing provisions and agreements, the Company has been
informed that in the opinion of the staff of the Commission such indemnification
is against public policy as expressed in the Securities Act and is therefore
unenforceable.

Item 7. Exemption from Registration Claimed.

      This item is not applicable.


                                      II-2
<PAGE>   6

Item 8. Exhibits.

      The following exhibits are filed as part of this Registration Statement or
incorporated by reference herein:

Exhibit Number                      Description of Exhibits
--------------                      -----------------------

      4.1(a)      Restated Certificate of Incorporation of the Company (filed as
                  Exhibit 3.1 to the Company's Annual Report on Form 10-K (File
                  No. 0-15144) for the year ended September 30, 1995 and
                  incorporated herein by reference).

      4.1(b)      Amendment dated March 18, 1996 to Restated Certificate of
                  Incorporation of the Company (filed as Exhibit 4.1(c) to the
                  Company's Registration Statement on Form S-8 (File No.
                  333-35169) and incorporated herein by reference).

      4.2         Amended By-laws of the Company, as of April 24, 1997 (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-8 (File No. 333-35169) and incorporated herein by
                  reference).

      4.3         Form of certificate for the Company's common stock (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-1 (File No. 33-67576) and incorporated herein by reference).

      4.4*        Gartner Group, Inc. 1991 Stock Option Plan, as amended
                  effective October 13, 1998.

      5.1*        Opinion of Shipman & Goodwin LLP.

      23.1*       Independent Auditors' Consent, KPMG LLP.

      23.2*       Consent of Shipman & Goodwin LLP (included in Exhibit 5).

      24.1*       Powers of Attorney.

-------------
* Filed herewith.


                                      II-3
<PAGE>   7

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 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 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 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.

(c) Insofar as indemnification of 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>   8

                                   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 Stamford and State of Connecticut on the 26th
day of April, 1999.

                                       GARTNER GROUP, INC.


                                       BY  /s/ William T. Clifford
                                           -------------------------------------
                                           William T. Clifford
                                           President and Chief Executive Officer

      Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed below by the following persons in
the capacities and on the date indicated.

         Signature                         Title                       Date
         ---------                         -----                       ----

 /s/ William T. Clifford     President, Chief Executive Officer   April 26, 1999
--------------------------              and Director         
    William T. Clifford        (principal executive officer) 


 /s/ Michael D. Fleisher         Chief Financial Officer and      April 26, 1999
--------------------------  Executive Vice President-Finance and     
    Michael D. Fleisher           Administration (principal     
                              financial and accounting officer) 


   Manuel A. Fernandez*            Chairman of the Board          April 26, 1999
--------------------------
    Manuel A. Fernandez


     William A. Grabe*                    Director                April 26, 1999
--------------------------
     William O. Grabe


      Max D. Hopper*                      Director                April 26, 1999
--------------------------
       Max D. Hopper


    John P. Imlay, Jr.*                   Director                April 26, 1999
--------------------------
    John P. Imlay, Jr.


                                      II-5
<PAGE>   9


     Stephen G. Pagliuca*                 Director                April 26, 1999
------------------------------
      Stephen G. Pagliuca


       Dennis G. Sisco*                   Director                April 26, 1999
------------------------------
        Dennis G. Sisco


                                          Director
------------------------------
      Robert E. Weissman

*By: /s/ Michael D. Fleisher                                      April 26, 1999
------------------------------
        Michael D. Fleisher
          Attorney-in-Fact


                                      II-6
<PAGE>   10

                                  EXHIBIT INDEX

Exhibit Number                      Description of Exhibits
--------------                      -----------------------

      4.1(a)      Restated Certificate of Incorporation of the Company (filed as
                  Exhibit 3.1 to the Company's Annual Report on Form 10-K (File
                  No. 0-15144) for the year ended September 30, 1995 and
                  incorporated herein by reference).

      4.1(b)      Amendment dated March 18, 1996 to Restated Certificate of
                  Incorporation of the Company (filed as Exhibit 4.1(c) to the
                  Company's Registration Statement on Form S-8 (File No.
                  333-35169) and incorporated herein by reference).

      4.2         Amended By-laws of the Company, as of April 24, 1997 (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-8 (File No. 333-35169) and incorporated herein by
                  reference).

      4.3         Form of certificate for the Company's common stock (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-1 (File No. 33-67576) and incorporated herein by reference).

      4.4*        Gartner Group, Inc. 1991 Stock Option Plan, as amended
                  effective October 13, 1998.

      5.1*        Opinion of Shipman & Goodwin LLP.

      23.1*       Independent Auditors' Consent, KPMG LLP.

      23.2*       Consent of Shipman & Goodwin LLP (included in Exhibit 5).

      24.1*       Powers of Attorney.

-------------
* Filed herewith.
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 20223}]
{"company-data": {"conformed-name": "GARTNER GROUP INC", "cik": "0000749251", "assigned-sic": "8741", "irs-number": "043099750", "state-of-incorporation": "DE", "fiscal-year-end": "0930"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-77015", "film-number": "99600897"}, "business-address": {"street1": "56 TOP GALLANT RD", "street2": "P O BOX 10212", "city": "STAMFORD", "state": "CT", "zip": "06904-2212", "phone": "2039640096"}}
1

     As filed with the Securities and Exchange Commission on April 26, 1999

                                                   Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

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

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

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

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

                 Delaware                                      04-3099750
      (State or other jurisdiction of                       (I.R.S. Employer
      incorporation or organization)                       Identification No.)

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

               P.O. Box 10212
             56 Top Gallant Road
            Stamford, Connecticut                               06904-2212
  (Address of  Principal Executive Offices)                     (Zip Code)

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

                   Gartner Group, Inc. 1991 Stock Option Plan
                            (Full title of the plan)

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

                               Michael D. Fleisher
              Chief Financial Officer and Executive Vice President-
                           Finance and Administration
                               Gartner Group, Inc.
                               56 Top Gallant Road
                             Stamford, CT 06904-2212
                     (Name and address of agent for service)

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

                                 (203) 964-0096
          (Telephone number, including area code, of agent for service)

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

                                    Copy to:

                            Michael J. Palmieri, Esq.
                              Shipman & Goodwin LLP
                               One Landmark Square
                               Stamford, CT 06901
                                 (203) 324-8100
CALCULATION OF REGISTRATION FEE
==============================================================================================
                                                   Proposed        Proposed
                                                    Maximum         Maximum
     Title of Each Class           Amount          Offering        Aggregate     Amount of
     of Securities to be           to be           Price per       Offering     Registration
          Registered             Registered          Share         Price (1)        Fee
----------------------------------------------------------------------------------------------
Common Stock, Class A, par    3,110,914 shares      $21.86       $ 68,003,942      $18,906
value $0.0005 (currently
outstanding options) (1)
----------------------------------------------------------------------------------------------
Common Stock, Class A, par      100,000 shares      $19.3125     $  1,931,250      $   537
value $0.0005 (allocated
shares of restricted stock)
(2)
----------------------------------------------------------------------------------------------
Common Stock, Class A, par    6,789,086 shares      $19.3125     $131,114,223      $36,450
value $0.0005 (shares
available for future
issuance) (2)
----------------------------------------------------------------------------------------------
2

----------------------------------------------------------------------------------------------
Total                                                                            $55,893
----------------------------------------------------------------------------------------------
(1)   In accordance with Rule 457(h), the computation is based on the weighted
      average exercise price per share of $21.86 as to 3,110,914 outstanding but
      unexercised options to purchase Common Stock under the 1991 Stock Option
      Plan.
(2)   In accordance with Rule 457(h), the Proposed Maximum Offering Price per
      Share as to the 100,000 shares of restricted stock to be issued under the
      1991 Stock Option Plan and the remaining 6,789,086 shares of Common Stock
      authorized for issuance pursuant to the 1991 Stock Option Plan has been
      estimated in accordance with Rule 457(c) under the Securities Act of 1933,
      solely for the purpose of calculating the registration fee. The
      computation is based on the average of the high and low price of the
      Common Stock as reported on the New York Stock Exchange on April 21, 1999.
--------------------------------------------------------------------------------
 Pursuant to Rule 429 under the Securities Act of 1933, the prospectus relating
 to the securities registered under this Registration Statement also relates to
                      Registration Statement No. 33-85926.
================================================================================
3

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

      The information statement being delivered by Gartner Group, Inc. (the
"Company") to participants in the Company's 1991 Stock Option Plan (the "Plan"),
as required by Rule 428 under the Securities Act of 1933, as amended (the
"Securities Act"), has been prepared in accordance with the requirements of Form
S-8 and relates to shares of common stock, par value $0.0005 per share, (the
"Shares") issued or to be issued pursuant to the Plan. The information with
respect to the Plan required in the Section 10(a) prospectus is included in
documents being maintained and delivered by the Company as required by Rule 428
under the Securities Act. The Company shall provide to participants a written
statement advising them of the availability without charge, upon written or oral
request, of documents incorporated by reference herein, as is required by Item 2
of Part I of Form S-8.
4

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

      The following documents, previously filed with the Commission, are hereby
incorporated by reference in this registration statement:

      (a) The Company's Annual Report on Form 10-K for the year ended September
30, 1998;

      (b) The Company's Quarterly Report on Form 10-Q for the quarter ended
December 31, 1998; and

      (c) The description of the Shares contained in the Registration Statement
on Form 8-A filed on August 24, 1998, filed pursuant to Section 12(b) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), including any
amendment or report filed for the purpose of updating such description.

      In addition, all documents subsequently filed by the Company pursuant to
Section 13(a), 13(c), 14 or 15(d) of the Exchange Act on or after the date of
this Registration Statement and prior to the filing of a post-effective
amendment which indicates that all securities offered hereby 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 a part hereof
from the date of filing of such documents. Any statement contained in a document
incorporated or deemed to be incorporated by reference in this registration
statement 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 so modified or superseded,
to constitute a part of this registration statement.

Item 4. Description of Securities.

      This item is not applicable.

Item 5. Interests of Named Experts and Counsel.

      This item is not applicable.

Item 6. Indemnification of Directors and Officers.
5

      Section 145 of the Delaware General Corporation Law ("Delaware Law")
provides that a corporation may indemnify a director, officer, employee or agent
made a party to an action by reason of the fact that he was a director, officer,
employee or agent of the corporation, or was serving at the request of the
corporation, against expenses actually and reasonably incurred, including
attorneys' fees, in connection with such action, if he acted in good faith and
in a manner he reasonably believed to be in, or not opposed to, the best
interests of the corporation and, with respect to any criminal action, had no
reasonable cause to believe his conduct was unlawful.

      The Company's Certificate of Incorporation limits, to the maximum extent
permitted by Delaware Law, the personal liability of a director to the Company
or its shareholders for monetary damages for breach of fiduciary duty as a
director. The Company's By-laws provide that the Company shall indemnify its
officers and directors to the fullest extent permitted by Delaware Law against
all expense, liability and loss, including attorneys' fees, actually and
reasonably incurred and may purchase and maintain insurance against any
liability asserted and incurred by reason of serving as such, whether or not the
Company has the power to indemnify against such liability. The Company has
entered into indemnification agreements with its officers and directors
containing provisions which are in some respects broader than the specific
indemnification provisions contained in Delaware Law and which require that, to
the extent the Company maintains liability insurance applicable to officers or
directors, each officer and director shall be covered by such policies to the
same extent as are accorded the most favorably insured of the Company's officers
or directors, as the case may be.

      Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers or persons controlling the Company
pursuant to the foregoing provisions and agreements, the Company has been
informed that in the opinion of the staff of the Commission such indemnification
is against public policy as expressed in the Securities Act and is therefore
unenforceable.

Item 7. Exemption from Registration Claimed.

      This item is not applicable.

                                      II-2
6

Item 8. Exhibits.

      The following exhibits are filed as part of this Registration Statement or
incorporated by reference herein:

Exhibit Number                      Description of Exhibits
--------------                      -----------------------

      4.1(a)      Restated Certificate of Incorporation of the Company (filed as
                  Exhibit 3.1 to the Company's Annual Report on Form 10-K (File
                  No. 0-15144) for the year ended September 30, 1995 and
                  incorporated herein by reference).

      4.1(b)      Amendment dated March 18, 1996 to Restated Certificate of
                  Incorporation of the Company (filed as Exhibit 4.1(c) to the
                  Company's Registration Statement on Form S-8 (File No.
                  333-35169) and incorporated herein by reference).

      4.2         Amended By-laws of the Company, as of April 24, 1997 (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-8 (File No. 333-35169) and incorporated herein by
                  reference).

      4.3         Form of certificate for the Company's common stock (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-1 (File No. 33-67576) and incorporated herein by reference).

      4.4*        Gartner Group, Inc. 1991 Stock Option Plan, as amended
                  effective October 13, 1998.

      5.1*        Opinion of Shipman & Goodwin LLP.

      23.1*       Independent Auditors' Consent, KPMG LLP.

      23.2*       Consent of Shipman & Goodwin LLP (included in Exhibit 5).

      24.1*       Powers of Attorney.

-------------
* Filed herewith.

                                      II-3
7

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 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 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 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.

(c) Insofar as indemnification of 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
8

                                   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 Stamford and State of Connecticut on the 26th
day of April, 1999.

                                       GARTNER GROUP, INC.

                                       BY  /s/ William T. Clifford
                                           -------------------------------------
                                           William T. Clifford
                                           President and Chief Executive Officer

      Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed below by the following persons in
the capacities and on the date indicated.

         Signature                         Title                       Date
         ---------                         -----                       ----

 /s/ William T. Clifford     President, Chief Executive Officer   April 26, 1999
--------------------------              and Director         
    William T. Clifford        (principal executive officer) 

 /s/ Michael D. Fleisher         Chief Financial Officer and      April 26, 1999
--------------------------  Executive Vice President-Finance and     
    Michael D. Fleisher           Administration (principal     
                              financial and accounting officer) 

   Manuel A. Fernandez*            Chairman of the Board          April 26, 1999
--------------------------
    Manuel A. Fernandez

     William A. Grabe*                    Director                April 26, 1999
--------------------------
     William O. Grabe

      Max D. Hopper*                      Director                April 26, 1999
--------------------------
       Max D. Hopper

    John P. Imlay, Jr.*                   Director                April 26, 1999
--------------------------
    John P. Imlay, Jr.

                                      II-5
9

     Stephen G. Pagliuca*                 Director                April 26, 1999
------------------------------
      Stephen G. Pagliuca

       Dennis G. Sisco*                   Director                April 26, 1999
------------------------------
        Dennis G. Sisco

                                          Director
------------------------------
      Robert E. Weissman

*By: /s/ Michael D. Fleisher                                      April 26, 1999
------------------------------
        Michael D. Fleisher
          Attorney-in-Fact

                                      II-6
10

                                  EXHIBIT INDEX

Exhibit Number                      Description of Exhibits
--------------                      -----------------------

      4.1(a)      Restated Certificate of Incorporation of the Company (filed as
                  Exhibit 3.1 to the Company's Annual Report on Form 10-K (File
                  No. 0-15144) for the year ended September 30, 1995 and
                  incorporated herein by reference).

      4.1(b)      Amendment dated March 18, 1996 to Restated Certificate of
                  Incorporation of the Company (filed as Exhibit 4.1(c) to the
                  Company's Registration Statement on Form S-8 (File No.
                  333-35169) and incorporated herein by reference).

      4.2         Amended By-laws of the Company, as of April 24, 1997 (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-8 (File No. 333-35169) and incorporated herein by
                  reference).

      4.3         Form of certificate for the Company's common stock (filed as
                  Exhibit 4.2 to the Company's Registration Statement on Form
                  S-1 (File No. 33-67576) and incorporated herein by reference).

      4.4*        Gartner Group, Inc. 1991 Stock Option Plan, as amended
                  effective October 13, 1998.

      5.1*        Opinion of Shipman & Goodwin LLP.

      23.1*       Independent Auditors' Consent, KPMG LLP.

      23.2*       Consent of Shipman & Goodwin LLP (included in Exhibit 5).

      24.1*       Powers of Attorney.

-------------
* Filed herewith.