FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * SUMMIT PARTNERS L P   2. Issuer Name and Ticker or Trading Symbol NightHawk Radiology Holdings Inc [NHWK] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner _____ Officer (give title below) __X__ Other (specify below) Manager of GP of 10% Owner (Last) (First) (Middle) 222 BERKELEY STREET, 18TH FLOOR 3. Date of Earliest Transaction (Month/Day/Year) 10/31/2006 (Street) BOSTON, MA 02116 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 10/31/2006   S   4,500,000 (1) D $ 18.5 0 I See Footnote and Remarks (1)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
SUMMIT PARTNERS L P 222 BERKELEY STREET 18TH FLOOR BOSTON, MA 02116				Manager of GP of 10% Owner
SUMMIT PARTNERS VI GP LLC 222 BERKELEY STREET 18TH FLOOR BOSTON, MA 02116				Indirect GP of 10% Owner
SUMMIT PARTNERS VI GP LP 222 BERKELEY STREET 18TH FLOOR BOSTON, MA 02116				GP of 10% Owner
SUMMIT PARTNERS SD II LLC C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116				GP of Owner

Signatures

Summit Partners, L.P., by Summit Master Company, LLC, Its General Partner, by Robin W. Devereux, Power of Attorney for Walter G. Kortschak, Member		10/31/2006
**Signature of Reporting Person		Date
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 Walter G. Kortschak, Member		10/31/2006
**Signature of Reporting Person		Date
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 Walter G. Kortschak, Member		10/31/2006
**Signature of Reporting Person		Date
Summit Partners SD II, LLC, by Stamps, Woodsum & Co., IV, by Robin W. Devereux, Power of Attorney for Martin J. Mannion, Member		10/31/2006
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	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.
Remarks: 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.

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