X0202 4 2006-02-10 0 0001292470 NightHawk Radiology Holdings Inc NHWK 0000830588 SUMMIT PARTNERS L P 222 BERKELEY STREET 18TH FLOOR BOSTON MA 02116 0 0 0 1 Manager of GP of 10% Owner 0001258825 SUMMIT PARTNERS VI GP LLC 222 BERKELEY STREET 18TH FLOOR BOSTON MA 02116 0 0 0 1 Indirect GP of 10% Owner 0001258826 SUMMIT PARTNERS VI GP LP 222 BERKELEY STREET 18TH FLOOR BOSTON MA 02116 0 0 0 1 GP of 10% Owner 0001032090 SUMMIT PARTNERS SD II LLC C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 0 0 0 1 GP of Owner Common Stock 2006-02-10 4 S 0 600003 16.00 D 5400000 I See Footnotes Represents shares beneficially held by Summit Ventures VI-A, L.P., Summit Ventures VI-B, L.P., Summit VI Advisors Fund, L.P., Summit VI Entrepreneurs Fund, L.P., Summit Subordinated Debt Fund II, L.P., and Summit Investors VI, L.P. Summit Partners, L.P. is the managing member of Summit Partners VI (GP), LLC, which is the general partner of Summit Partners VI (GP), L.P., which is the general partner of each of Summit Ventures VI-A, L.P., Summit Ventures VI-B, L.P., Summit VI Advisors Fund, L.P., Summit VI Entrepreneurs Fund, L.P. and Summit Investors VI, L.P. Summit Partners, L.P. is the managing member of Stamps, Woodsum & Co., IV, which is the general partner of Summit Partners SD II, LLC, which is the general part of Summit Subordinated Debt Fund II, L.P. Summit Partners, L.P. is the managing member of Summit Partners VI (GP), LLC, which is the general partner of Summit Partners VI (GP), L.P., which is the general partner of each of Summit Ventures VI-A, L.P., Summit Ventures VI-B, L.P., Summit VI Advisors Fund, L.P., Summit VI Entrepreneurs Fund, L.P. and Summit Investors VI, L.P. Summit Partners, L.P. is the managing member of Stamps, Woodsum & Co, IV, which is the general partner of Summit Partners SD II, LLC, which is the general partner of Summit Subordinated Debt Fund, L.P. Summit Partners, L.P. has voting and dispositive authority over the shares held by each of these entities and, therefore, may beneficially own such shares. Each of Summit Partners, L.P., Summit Partners VI (GP), LLC, Summit Partners VI (GP), L.P., Summit Partners SD II, LLC, and Summit Master Company, LLC, which is the general partner of Summit Partners, L.P., disclaims beneficial ownership of such shares, except to the extent of its pecuniary interest. Summit Partners, L.P., by Summit Master Company, LLC, Its General Partner, by Robin W. Devereux, Power of Attorney for Peter Y. Chung, Member 2006-02-10 Summit Partners VI (GP), LLC, by Summit Partners, L.P., its General Partner, by Summit Master Company, LLC, its General Partner, by Robin W. Devereux, Power of Attorney for Peter Y. Chung, Member 2006-02-10 Summit Partners VI (GP), L.P., by Summit Partners VI (GP), LLC, its General Partner, by Summit Partners L.P., its General Partner, by Summit Master Company, LLC, its General Partner, by Robin W. Devereux, Power of Attorney for Peter Y. Chung, Member 2006-02-10 Summit Partners SD II, LLC, by Stamps, Woodsum & Co., IV, Its General Partner, by Summit Partners, L.P., Its General Partner, by Summit Master Company, LLC, Irs General Partner, by Robin W. Devereux, Power of Attorney for Peter Y. Chung, Member 2006-02-10