SEATTLE, WA – December 15, 2006 – Isilon Systems, Inc. (Nasdaq: ISLN) today announced an initial public offering of 8,350,000 shares of its common stock at a price of $13 per share. Isilon and several of its stockholders have granted the underwriters a 30-day option to purchase up to 1,252,500 additional shares to cover over-allotments. Isilon’s common stock will be listed on the Nasdaq Global Market under the symbol “ISLN” and will begin trading Friday, December 15, 2006.

Morgan Stanley & Co. Incorporated and Merrill Lynch, Pierce, Fenner & Smith, Inc. acted as joint book-running managers for the offering with Needham & Company, LLC and RBC Capital Markets Corporation serving as co-managers. A copy of the final prospectus relating to the offering may be obtained by contacting Morgan Stanley & Co. Incorporated, 180 Varick Street, New York, NY 10014, Attention: Prospectus Department, by telephone at 212 761 6775 or by e-mail at prospectus@morganstanley.com, or by contacting Merrill Lynch, Pierce, Fenner & Smith, Inc., 4 World Financial Center, North Tower, New York, New York 10080, by telephone at 212-449-1000.