COSTAR GROUP, INC. — Director's Dealing 2011

Nov 3, 2011

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: COSTAR GROUP INC (CSGP)
CIK: 0001057352
Period of Report: 2011-11-01

Reporting Person: FLORANCE ANDREW C (Director, President and CEO)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2011-11-01	Common Stock, par value $0.01 per share	M	45074	$20.30	Acquired	251618	Direct
2011-11-01	Common Stock, par value $0.01 per share	S	45074	$59.33	Disposed	206544	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2011-11-01	Option to Acquire Common Stock	$20.30	M	45074	Disposed	2012-06-03	Common Stock (45074)	Direct

Footnotes

F1: Represents all shares of Common Stock owned, consisting of 213,150 shares of Common Stock and 38,468 shares of Common Stock subject to unvested Restricted Stock Grants.

F2: Average based on sales prices ranging from $58.35 to $61.11.

F3: Represents all shares of Common Stock owned, consisting of 168,076 shares of Common Stock and 38,468 shares of Common Stock subject to unvested Restricted Stock Grants.

F4: The option vested in four equal installments on June 4, 2003, June 4, 2004, June 4, 2005 and June 4, 2006.