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 * Lucas Donald A   2. Issuer Name and Ticker or Trading Symbol DEXCOM INC [DXCM] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 2440 SAN HILL RD., SUITE 100 3. Date of Earliest Transaction (Month/Day/Year) 08/14/2006 (Street) MENLO PARK, CA 94025 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ 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 08/14/2006   D V 80 D $ 22.04 18,561 D (1)   Common Stock 08/14/2006   D V 45 D $ 22.3 18,516 D (1)   Common Stock 08/14/2006   D V 363 D $ 13.79 18,153 D (1)   Common Stock 08/14/2006   A V 80 A $ 22.04 80 I (1) RWI Ventures Service Company, L.L.C. Common Stock 08/14/2006   A V 45 A $ 22.3 125 I (1) RWI Ventures Service Company, L.L.C. Common Stock 08/14/2006   A V 363 A $ 13.79 488 I RWI Ventures Service Company, L.L.C. Common Stock               793,490 I RWI Ventures I, L.P. (2) Common Stock               60,823 I RWI Group III, L.P. (2)

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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

Stock Option (Right to Buy)

$ 12

(3)

04/15/2006

Common Stock

25,000

25,000

D

Stock Option (Right to Buy)

$ 20.38

(4)

04/13/2016

Common Stock

10,000

35,000

D

Stock Option (Right to Buy)

$ 21.81

(4)

06/15/2016

Common Stock

10,000

45,000

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Lucas Donald A 2440 SAN HILL RD. SUITE 100 MENLO PARK, CA 94025	X

Signatures

/s/ Donald A. Lucas		08/14/2006
**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)	These securities were transferred from the reporting person to RWI Ventures Service Co., L.L.C. without consideration. The reporting person is a managing member of RWI Ventures Service Co., L.L.C. and disclaims beneficial ownership of these shares except to his pecuniary interest therein.
(2)	The Reporting Person is a Managing Director of RWI Ventures (RWI). As a Managing Director, the Reporting Person shares voting and investment power of the shares held by RWI Group III L.P. and RWI Ventures I L.P., which are affiliated with RWI. The Reporting Person disclaims beneficial ownership of these shares except to his pecuniary interest therein.
(3)	The option vests and becomes exercisable with respect to 1/3rd of the shares one year after the date of grant and thereafter continues to vest and become exercisable as to 1/36th of the remaining shares each month thereafter (with the shares being fully vested on the 3rd anniversary of the date of grant).
(4)	The option vests and becomes exercisable as to 1/36th each month beginning one month following the date of grant and becomes fully vested on the third anniversary of the date of grant.

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