UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934

                               (Amendment No. 1 )*

                                   Dexcom Inc.
                                (Name of Issuer)

                                  Common Stock
                         (Title of Class of Securities)

                                    252131107
                                 (CUSIP Number)

                                December 31, 2007
             (Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

     [X]  Rule 13d-1(b)

     [ ]  Rule 13d-1(c)

     [ ]  Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



                                  SCHEDULE 13G

CUSIP No.  252131107

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           1.   Names of Reporting Persons. I.R.S. Identification Nos. of above
                persons (entities only).
                Invesco Ltd.

                   AIM Capital Management, Inc
                   AIM Advisors, Inc.

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           2.   Check the Appropriate Box if a Member of a Group (see
                Instructions)
                (a)
                (b)

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           3.   SEC Use Only  _______________________________________________

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           4.   Citizenship or Place of Organization
                Invesco Ltd. - Bermuda

                   AIM Capital Management, Inc - US
                   AIM Advisors, Inc. - US

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                      5.   Sole Voting Power 1,145,835: Such
                           shares are held by the following
                           entities in the respective amounts
                           listed:

                           AIM Capital Management, Inc - 198,771
                           AIM Advisors, Inc. - 947,064

Number of Shares      ----------------------------------------------------------
Beneficially Owned
by Each Reporting     6.   Shared Voting Power   ______-0-______
Person With

                      ----------------------------------------------------------

                      7.   Sole Dispositive Power 1,145,835:
                           Such shares are held by the
                           following entities in the respective
                           amounts listed:

                           AIM Capital Management, Inc - 198,771
                           AIM Advisors, Inc. - 947,064

                      ----------------------------------------------------------

                      8.   Shared Dispositive Power   ______-0-______

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           9.   Aggregate Amount Beneficially Owned by Each Reporting Person:
                1,145,835

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           10.  Check if the Aggregate Amount in Row (9) Excludes Certain Shares
                (See Instructions) N/A

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           11.  Percent of Class Represented by Amount in Row (9)        4.05%
                                                                         ----

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           12.  Type of Reporting Person (See Instructions)
                IA, HC. See Items 2 and 3 of this statement.



                                  SCHEDULE 13G

Item 1(a)          Name of Issuer:

                      Dexcom Inc.

Item 1(b)          Address of Issuer's Principal Executive Offices:

                      5555 Oberlin Drive
                      San Diego, CA
                      United States

Item 2(a)          Name of Person Filing:

                   Invesco Ltd.

                   In accordance with Securities and Exchange Commission Release
                   No. 34-39538 (January 12, 1998), this statement on Schedule
                   13G or amendment thereto is being filed by Invesco Ltd.
                   ("Invesco"), a Bermuda Company, on behalf of itself and its
                   subsidiaries listed in Item 4 of the cover of this statement.
                   Invesco through such subsidiaries provides investment
                   management services to institutional and individual investors
                   worldwide.

                   Executive officers and directors of Invesco or its
                   subsidiaries may beneficially own shares of the securities of
                   the issuer to which this statement relates (the "Shares"),
                   and such Shares are not reported in this statement. Invesco
                   and its subsidiaries disclaim beneficial ownership of Shares
                   beneficially owned by any of their executive officers and
                   directors. Each of Invesco's direct and indirect subsidiaries
                   also disclaim beneficial ownership of Shares beneficially
                   owned by Invesco and any other subsidiary.

Item 2(b)          Address of Principal Business Office:

                   1360 Peachtree Street NE
                   Atlanta, GA 30309
                   United States

Item 2(c)          Citizenship:
                   See the response to Item 2(a) of this statement.

Item 2(d)          Title of Class of Securities:

                   Common Stock, $.001 par value per share

Item 2(e)          CUSIP Number:

                   252131107

Item 3             If this statement is filed pursuant to ss240.13d-1(b) or
                   240.13d-2(b) or (c), check whether the person filing is a:

           (e) [x] An investment adviser in accordance with section
                   240.13d-1(b)(1)(ii)(E)

           (g) [x] A parent holding company or control person in accordance with
                   section 240.13d-1(b)(1)(ii)(G)

                   As noted in Item 2 above, Invesco is making this filing on
                   behalf of its subsidiaries listed herein. Each of these
                   entities is either an investment adviser registered with the
                   United States Securities and Exchange Commission under
                   Section 203 of the Investment Advisers Act of 1940, as
                   amended, or under similar laws of other jurisdictions.
                   Invesco is a holding company.



Item 4             Ownership:

                   Please see responses to Items 5-8 on the cover of this
                   statement, which are incorporated herein by reference.

Item 5             Ownership of Five Percent or Less of a Class:

                   If this statement is being filed to report the fact that as
                   of the date hereof the reporting person has ceased to be the
                   beneficial owner of more than five percent of the class of
                   securities, check the following [x]

Item 6             Ownership of More than Five Percent on Behalf of Another
                   Person:

                   N/A

Item 7             Identification and Classification of the Subsidiary Which
                   Acquired the Security Being reported on By the Parent Holding
                   Company:

                   Please see Item 3 of this statement, which is incorporated
                   herein by reference.

Item 8             Identification and Classification of Members of the Group:

                   N/A

Item 9             Notice of Dissolution of a Group:

                   N/A

Item 10            Certification:

                   By signing below I certify that, to the best of my knowledge
                   and belief, the securities referred to above were acquired
                   and are held in the ordinary course of business and were not
                   acquired and are not held for the purpose of or with the
                   effect of changing or influencing the control of the issuer
                   of the securities and were not acquired and are not held in
                   connection with or as a participant in any transaction having
                   that purpose or effect.

                   Signature:

                   After reasonable inquiry and to the best of my knowledge and
                   belief, I certify that the information set forth in this
                   statement is true, complete and correct.

                                        02/09/2008
                                        Date

                                        Invesco Ltd.


                                        By: /s/ Lisa Brinkley
                                            ------------------------------------
                                            Lisa Brinkley
                                            Global Compliance Director