<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
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    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001191307</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
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      <liveTestFlag>LIVE</liveTestFlag>


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    <issuerInfo>
      <issuerCik>0001093557</issuerCik>
      <issuerName>DEXCOM INC</issuerName>
      <secFileNumber>000-51222</secFileNumber>
      <issuerAddress>
        <com:street1>6340 SEQUENCE DRIVE</com:street1>
        <com:city>SAN DIEGO</com:city>
        <com:stateOrCountry>CA</com:stateOrCountry>
        <com:zipCode>92121</com:zipCode>
      </issuerAddress>
      <issuerContactPhone>8582000200</issuerContactPhone>
      <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>ALTMAN STEVEN R</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
      <relationshipsToIssuer>
        <relationshipToIssuer>Director</relationshipToIssuer>
      </relationshipsToIssuer>
    </issuerInfo>
    <securitiesInformation>
      <securitiesClassTitle>COMMON</securitiesClassTitle>
      <brokerOrMarketmakerDetails>
        <name>THE CHARLES SCHWAB CORPORATION</name>
        <address>
          <com:street1>3000 Schwab Way</com:street1>
          <com:city>Westlake</com:city>
          <com:stateOrCountry>TX</com:stateOrCountry>
          <com:zipCode>76262</com:zipCode>
        </address>
      </brokerOrMarketmakerDetails>
      <noOfUnitsSold>6000</noOfUnitsSold>
      <aggregateMarketValue>664485.00</aggregateMarketValue>
      <noOfUnitsOutstanding>387871796</noOfUnitsOutstanding>
      <approxSaleDate>09/15/2023</approxSaleDate>
      <securitiesExchangeName>NASDAQ</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>COMMON</securitiesClassTitle>
      <acquiredDate>05/21/2020</acquiredDate>
      <natureOfAcquisitionTransaction>RSU</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>ISSUER</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>6000</amountOfSecuritiesAcquired>
      <paymentDate>05/21/2020</paymentDate>
      <natureOfPayment>NA</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <remarks>FULL ACCOUNT TITLE: S &amp; L ALTMAN TTEE ALTMAN FAMILY TRUST SHARES ACQUIRED VIA FOLLOWING DATE RANGE: 5/21/2020 TO 5/21/2022.</remarks>
    <noticeSignature>
      <noticeDate>09/15/2023</noticeDate>
      <planAdoptionDates>
        <planAdoptionDate>05/30/2023</planAdoptionDate>
      </planAdoptionDates>
      <signature>STEVEN R. ALTMAN</signature>
    </noticeSignature>
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144
0001191307
XXXXXXXX
LIVE
0001093557
DEXCOM INC
000-51222
6340 SEQUENCE DRIVE
SAN DIEGO
CA
92121
8582000200
ALTMAN STEVEN R
Director
COMMON
THE CHARLES SCHWAB CORPORATION
3000 Schwab Way
Westlake
TX
76262
6000
664485.00
387871796
09/15/2023
NASDAQ
COMMON
05/21/2020
RSU
ISSUER
N
6000
05/21/2020
NA
Y
FULL ACCOUNT TITLE: S & L ALTMAN TTEE ALTMAN FAMILY TRUST SHARES ACQUIRED VIA FOLLOWING DATE RANGE: 5/21/2020 TO 5/21/2022.
09/15/2023
05/30/2023
STEVEN R. ALTMAN