COSTAR GROUP, INC. — Director's Dealing 2010

Apr 1, 2010

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: COSTAR GROUP INC (CSGP)
CIK: 0001057352
Period of Report: 2010-03-31

Reporting Person: BONDERMAN DAVID (Director)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2010-03-31	Common Stock, par value $0.01 per share	M	1000	$24.875	Acquired	270008	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2010-03-31	Option to acquire Common Stock	$24.875	M	1000	Disposed	2010-06-20	Common Stock (1000)	Direct

Footnotes

F1: Represents all shares of Common Stock owned, consisting of 265,926 shares of Common Stock and 4,082 shares of Common Stock subject to unvested Restricted Stock Grants.

F2: The option vested in four equal installments on June 21, 2001, June 21, 2002, June 21, 2003 and June 21, 2004.