FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person *   Radecki Brian J 2. Date of Event Requiring Statement (Month/Day/Year) 06/05/2007 3. Issuer Name and Ticker or Trading Symbol COSTAR GROUP INC [CSGP] (Last) (First) (Middle) C/O COSTAR GROUP, INC., 2 BETHESDA METRO CENTER, 10TH FLOOR 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) Chief Financial Officer 5. If Amendment, Date Original Filed(Month/Day/Year) (Street) BETHESDA, MD 20814 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Beneficially Owned

1.Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5) Common Stock, par value $0.01 per share 6,815 (1) D Â

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Option to Acquire Common Stock	  (2)	12/01/2012	Common Stock, par value $0.01 per share	1,875	$ 18.28	D	Â
Option to Acquire Common Stock	  (3)	02/05/2014	Common Stock, par value $0.01 per share	6,000	$ 39.81	D	Â
Option to Acquire Common Stock	  (4)	01/28/2017	Common Stock, par value $0.01 per share	4,000	$ 48.25	D	Â

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Radecki Brian J C/O COSTAR GROUP, INC. 2 BETHESDA METRO CENTER, 10TH FLOOR BETHESDA, MD 20814	Â	Â	  Chief Financial Officer	Â

Signatures

/s/ Jonathan Coleman, Attorney-in-Fact		06/06/2007
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 5(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Represents all shares of Common Stock owned, consisting of 2,344 shares of Common Stock and 4,471 shares of Common Stock subject to unvested Restricted Stock Grants.
(2)	The option is currently exercisable.
(3)	The option vests in four equal installments. The first three installments vested on February 6, 2005, February 6, 2006 and February 6, 2007. The last installment vests on February 6, 2008.
(4)	The option vests in four equal installments on January 29, 2008, January 29, 2009, January 29, 2010 and January 29, 2011.

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