COSTAR GROUP, INC. — Director's Dealing 2010

Apr 29, 2010

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: COSTAR GROUP INC (CSGP)
CIK: 0001057352
Period of Report: 2010-04-27

Reporting Person: Marples Paul (Managing Director, FOCUS)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2010-04-27	Common Stock, par value $0.01 per share	S	3800	$45.01	Disposed	21018	Direct
2010-04-29	Common Stock, par value $0.01 per share	S	200	$45.00	Disposed	20818	Direct

Footnotes

F1: Average based on sale prices ranging from $45.00 to $45.06.

F2: Represents all shares of Common Stock owned, consisting of 12,184 shares of Common Stock and 8,834 shares of Common Stock subject to unvested Restricted Stock Grants.

F3: Represents all shares of Common Stock owned, consisting of 11,984 shares of Common Stock and 8,834 shares of Common Stock subject to unvested Restricted Stock Grants.