Ownership Submission
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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(Print or Type Responses)
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)
08/10/2006
(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 08/10/2006   D V 100 D $ 11.23 28,541 D  
Common Stock 08/10/2006   D V 600 D $ 11.25 27,941 D  
Common Stock 08/10/2006   D V 300 D $ 11.26 27,641 D  
Common Stock 08/10/2008   D V 300 D $ 11.27 27,341 D  
Common Stock 08/10/2006   D V 400 D $ 11.28 26,941 D  
Common Stock 08/10/2006   D V 400 D $ 11.29 26,541 D  
Common Stock 08/10/2006   D V 600 D $ 11.3 25,941 D  
Common Stock 08/10/2006   D V 400 D $ 11.31 25,541 D  
Common Stock 08/10/2006   D V 100 D $ 11.32 25,441 D  
Common Stock 08/10/2006   D V 228 D $ 11.34 25,213 D  
Common Stock 08/10/2006   D V 200 D $ 11.35 25,013 D  
Common Stock 08/10/2006   D V 172 D $ 11.37 24,841 D  
Common Stock 08/10/2006   D V 400 D $ 11.38 24,441 D  
Common Stock 08/10/2006   D V 100 D $ 11.39 24,341 D  
Common Stock 08/10/2006   D V 200 D $ 11.4 24,141 D  
Common Stock 08/10/2006   D V 400 D $ 11.41 23,741 D  
Common Stock 08/10/2006   D V 100 D $ 11.42 23,641 D  
Common Stock 08/11/2006   D V 100 D $ 11.27 23,541 D  
Common Stock 08/11/2006   D V 100 D $ 11.24 23,441 D  
Common Stock 08/11/2006   D V 700 D $ 11.23 22,741 D  
Common Stock 08/11/2006   D V 1,300 D $ 11.22 21,441 D  
Common Stock 08/11/2006   D V 200 D $ 11.21 21,241 D  
Common Stock 08/11/2006   D V 200 D $ 11.2 21,041 D  
Common Stock 08/11/2006   D V 21 D $ 11.19 21,020 D  
Common Stock 08/11/2006   D V 400 D $ 11.18 20,620 D  
Common Stock 08/11/2006   D V 1,179 D $ 11.17 19,441 D  
Common Stock 08/11/2006   D V 800 D $ 11.16 18,641 D  
Common Stock               793,490 I RWI Ventures I, L.P. (1)
Common Stock               60,823 I RWI Group III, L.P. (1)

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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               (2) 04/15/2015 Common Stock 25,000   25,000 D  
Stock Option (Right to Buy) $ 20.38               (3) 04/13/2016 Common Stock 10,000   35,000 D  
Stock Option (Right to Buy) $ 21.81               (3) 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   08/11/2006
**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) 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.
(2) 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).
(3) 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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