SCHEDULE 13G

Amendment No. 0
Gartner Group Incorporated
Class B common stock
Cusip # 366651206

Cusip # 366651206
Item 1:	Reporting Person - FMR Corp.
Item 4:	Commonwealth of Massachusetts
Item 5:	418,855
Item 6:	0
Item 7:	11,076,954
Item 8:	0
Item 9:	11,076,954
Item 11:	32.045%
Item 12:	    HC

Cusip # 366651206
Item 1:	Reporting Person - Edward C. Johnson 3d
Item 4:	United States of America
Item 5:	0
Item 6:	0
Item 7:	11,076,954
Item 8:	0
Item 9:	11,076,954
Item 11:	32.045%
Item 12:	IN

Cusip # 366651206
Item 1:	Reporting Person - Abigail P. Johnson
Item 4:	United States of America
Item 5:	None
Item 6:	None
Item 7:	11,076,954
Item 8:	None
Item 9:	11,076,954
Item 11:	32.045%
Item 12:	    IN


SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)


Item 1(a).	Name of Issuer:

		Gartner Group Incorporated

Item 1(b).	Name of Issuer's Principal Executive Offices:

		56 Top Gallant Road, P.O. Box 10212
		Stamford, CT  06904-2212

Item 2(a).	Name of Person Filing:

		FMR Corp.

Item 2(b).	Address or Principal Business Office or, if None,
Residence:

		82 Devonshire Street, Boston, Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		Class B common stock

Item 2(e).	CUSIP Number:

		366651206

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-
2(b) and the person filing, FMR Corp., is a parent holding company in
accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	11,076,954

	(b)	Percent of Class:	32.045%

	(c)	Number of shares as to which such person has:

	(i)	sole power to vote or to direct the vote:	418,855

	(ii)	shared power to vote or to direct the vote:	0

	(iii)	sole power to dispose or to direct the disposition of:
	11,076,954

	(iv)	shared power to dispose or to direct the disposition of:
	0




Item 5.	Ownership of Five Percent or Less of a CommonStock.

	Not applicable.

Item 6.	Ownership of More than Five Percent on Behalf of Another
Person.

	Various persons have the right to receive or the power to direct
the receipt of dividends from, or the proceeds from the sale of, the
Class B common stock of Gartner Group Incorporated.  The interest of
one person, Fidelity Contrafund, an investment company registered under
the Investment Company Act of 1940, in the Class B common stock of
Gartner Group Incorporated, amounted to 2,737,962 shares or 7.921% of
the total outstanding Class B common stock at October 31, 1999. The
interest of one person, Growth & Income Fund, an investment company
registered under the Investment Company Act of 1940, in the Class B
common stock of Gartner Group Incorporated, amounted to 3,232,338
shares or 9.351% of the total outstanding Class B common stock at
October 31, 1999.

Item 7.	Identification and Classification of the Subsidiary Which
Acquired the Security Being Reported on By the Parent Holding Company.

	See attached Exhibit(s) A, B, and C.

Item 8.	Identification and Classification of Members of the Group.

	Not Applicable. See attached Exhibit A.

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were acquired in the ordinary
course of business and were not acquired for the purpose of and do not
have the effect of changing or influencing the control of the issuer of
such securities and were not acquired in connection with or as a
participant in any transaction having such purpose or effect.

Signature

	After reasonable inquiry and to the best of my knowledge and
belief, I certify that the information set forth in this Schedule 13G
in connection with FMR Corp.'s beneficial ownership of the Class B
common stock of Gartner Group Incorporated at October 31, 1999 is true,
complete and correct.

	November 10, 1999
Date


	/s/Eric D. Roiter
Signature


	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect
	subsidiaries



SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)

	Pursuant to the instructions in Item 7 of Schedule 13G, Fidelity
Management & Research Company ("Fidelity"), 82 Devonshire Street,
Boston, Massachusetts 02109, a wholly-owned subsidiary of FMR Corp. and
an investment adviser registered under Section 203 of the Investment
Advisers Act of 1940, is the beneficial owner of 10,511,557 shares or
30.409% of the Class B common stock outstanding of Gartner Group
Incorporated  ("the Company") as a result of acting as investment
adviser to various investment companies registered under Section 8 of
the Investment Company Act of 1940.

	The ownership of one investment company, Fidelity Contrafund,
amounted to 2,737,962 shares or 7.921% of the Class B common stock
outstanding. Fidelity Contrafund has its principal business office at
82 Devonshire Street, Boston, Massachusetts 02109.

	The ownership of one investment company, Growth & Income Fund,
amounted to 3,232,338 shares or 9.351% of the Class B common stock
outstanding. Growth & Income Fund has its principal business office at
82 Devonshire Street, Boston, Massachusetts 02109.

	Edward C. Johnson 3d, FMR Corp., through its control of Fidelity,
and the funds each has sole power to dispose of the 10,511,557 shares
owned by the Funds.

	Neither FMR Corp. nor Edward C. Johnson 3d, Chairman of FMR
Corp., has the sole power to vote or direct the voting of the shares
owned directly by the Fidelity Funds, which power resides with the
Funds' Boards of Trustees.  Fidelity carries out the voting of the
shares under written guidelines established by the Funds' Boards of
Trustees.

	Fidelity Management Trust Company, 82 Devonshire Street, Boston,
Massachusetts 02109, a wholly-owned subsidiary of FMR Corp. and a bank
as defined in Section 3(a)(6) of the Securities Exchange Act of 1934,
is the beneficial owner of  479,772 shares or 1.388% of the Class B
common stock outstanding of the Company as a result of its serving as
investment manager of the institutional account(s).

	Edward C. Johnson 3d and FMR Corp., through its control of
Fidelity Management Trust Company, each has sole dispositive power over
479,772 shares and sole power to vote or to direct the voting of
333,230 shares, and no power to vote or to direct the voting of 146,542
shares of Class B common stock owned by the institutional account(s) as
reported above.

	Strategic Advisers, Inc., 82 Devonshire Street, Boston, MA 02109,
a wholly-owned subsidiary of FMR Corp. and an investment adviser
registered under Section 203 of the Investment Advisers Act of 1940,
provides investment advisory services to individuals. It does not have
sole power to vote or direct the voting of shares of certain securities
held for clients and has sole dispositive power over such securities.
As such, FMR Corp.'s beneficial ownership may include shares
beneficially owned through Strategic Advisers, Inc.

	Members of the Edward C. Johnson 3d family are the predominant
owners of Class B shares of common stock of FMR Corp., representing
approximately 49% of the voting power of FMR Corp.  Mr. Johnson 3d owns
12.0% and Abigail Johnson owns 24.5% of the aggregate outstanding
voting stock of FMR Corp.  Mr. Johnson 3d is Chairman of FMR Corp. and
Abigail P. Johnson is a Director of FMR Corp.  The Johnson family group
and all other Class B shareholders have entered into a shareholders'
voting agreement under which all Class B shares will be voted in
accordance with the majority vote of Class B shares.  Accordingly,
through their ownership of voting common stock and the execution of the
shareholders' voting agreement, members of the Johnson family may be
deemed, under the Investment Company Act of 1940, to form a controlling
group with respect to FMR Corp.

	Fidelity International Limited, Pembroke Hall, 42 Crowlane,
Hamilton, Bermuda, and various foreign-based subsidiaries provide
investment advisory and management services to a number of non-U.S.
investment companies (the "International Funds") and certain
institutional investors.  Fidelity International Limited is the
beneficial owner of 85,625 shares or 0.248% of the Class B common stock
outstanding of the Company. Additional information with respect to the
beneficial ownership of Fidelity International Limited is shown on
Exhibit B, page 9.

SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)

	Pursuant to instructions in Item 7 of Schedule 13G, this Exhibit
has been prepared  to identify Fidelity International Limited, Pembroke
Hall, 42 Crow Lane, Hamilton, Bermuda, a Bermudan joint stock company
incorporated for an unlimited duration by private act of the Bermuda
Legislature (FIL) and an investment adviser to various investment
companies (the "International Funds") and certain institutional
investors, as a beneficial owner of the 85,625 shares or 0.248% of the
Class B common stock outstanding of Gartner Group Incorporated.

	Prior to June 30, 1980, FIL was a majority-owned subsidiary of
Fidelity Management & Research Company (Fidelity), a wholly-owned
subsidiary of FMR Corp.  On that date, the shares of FIL held by
Fidelity were distributed, as a dividend,  to the shareholders of FMR
Corp.  FIL currently operates as an entity independent of FMR Corp. and
Fidelity.  The International Funds and FIL's other clients, with the
exception of Fidelity and an affiliated company of Fidelity, are non-
U.S. entities.

	A partnership controlled by Edward C. Johnson 3d and members of
his family owns shares of FIL voting stock with the right to cast
approximately 39.89% of the total votes which may be cast by all
holders of FIL voting stock.  Mr. Johnson 3d is Chairman of FMR Corp.
and FIL.  FMR Corp. and FIL are separate and independent corporate
entities, and their Boards of Directors are generally composed of
different individuals.  Other than when one serves as a sub adviser to
the other, their investment decisions are made independently, and their
clients are generally different organizations.

	FMR Corp. and FIL are of the view that they are not acting as a
"group" for purposes of Section 13(d) under the Securities Exchange Act
of 1934 (the "1934" Act) and that they are not otherwise required to
attribute to each other the "beneficial ownership" of securities
"beneficially owned" by the other corporation within the meaning of
Rule 13d-3 promulgated under the 1934 Act.  Therefore, they are of the
view that the shares held by the other corporation need not be
aggregated for purposes of Section 13(d). However, FMR Corp. is making
this filing on a voluntary basis as if all of the shares are
beneficially owned by FMR Corp. and FIL on a joint basis.

	FIL may continue to have the International Funds or other
accounts purchase shares subject to a number of factors, including,
among others, the availability of shares for sale at what FIL considers
to be reasonable prices and other investment opportunities that may be
available to the International Funds.

	FIL intends to review continuously the equity position of the
International Funds and other accounts in the Company.  Depending upon
its future evaluations of the business and prospects of the Company and
upon other developments, including, but not limited to, general
economic and business conditions and money market and stock market
conditions, FIL may determine to cease making additional purchases of
shares or to increase or decrease the equity interest in the Company by
acquiring additional shares, or by disposing of all or a portion of the
shares.

	FIL does not have a present plan or proposal which relates to or
would result in (i) an extraordinary corporate transaction, such as a
merger, reorganization, liquidation, or sale or transfer of a material
amount of assets involving the Company or any of its subsidiaries, (ii)
any change in the Company's present Board of Directors or management,
(iii) any material changes in the Company's present capitalization or
dividend policy or any other material change in the Company's business
or corporate structure, (iv) any change in the Company's charter or by-
laws, or (v) the Company's common stock becoming eligible for
termination of its registration pursuant to Section 12(g)(4) of the
1934 Act.

	FIL  has sole power to vote and the sole power to dispose of
85,625  shares.





 SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on November 10, 1999, agree and consent
to the joint filing on their behalf of this Schedule 13G in connection
with their beneficial ownership of the Class B common stock of Gartner
Group Incorporated at October 31, 1999.

FMR Corp.

By   /s/Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect
	subsidiaries

Edward C. Johnson 3d

By   /s/Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Edward C. Johnson 3d

Abigail P. Johnson

By   /s/Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Abigail P. Johnson

Fidelity Management & Research Company

By   /s/Eric D. Roiter
	Eric D. Roiter
	Senior V.P. and General Counsel

	Fidelity Contrafund

By   /s/Eric D. Roiter
	Eric D. Roiter
	Secretary

Growth & Income Fund

By   /s/Eric D. Roiter
	Eric D. Roiter
	Secretary