<SEC-DOCUMENT>0001093557-25-000153.txt : 20250512
<SEC-HEADER>0001093557-25-000153.hdr.sgml : 20250512
<ACCEPTANCE-DATETIME>20250512160854
ACCESSION NUMBER:		0001093557-25-000153
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20250508
FILED AS OF DATE:		20250512
DATE AS OF CHANGE:		20250512

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Malady Kyle
		CENTRAL INDEX KEY:			0001760581
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-51222
		FILM NUMBER:		25934843

	MAIL ADDRESS:	
		STREET 1:		1095 AVENUE OF THE AMERICAS
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10036

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			DEXCOM INC
		CENTRAL INDEX KEY:			0001093557
		STANDARD INDUSTRIAL CLASSIFICATION:	SURGICAL & MEDICAL INSTRUMENTS & APPARATUS [3841]
		ORGANIZATION NAME:           	08 Industrial Applications and Services
		EIN:				330857544
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		6340 SEQUENCE DRIVE
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92121
		BUSINESS PHONE:		8582000200

	MAIL ADDRESS:	
		STREET 1:		6340 SEQUENCE DRIVE
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92121
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wk-form4_1747080522.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-05-08</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001093557</issuerCik>
        <issuerName>DEXCOM INC</issuerName>
        <issuerTradingSymbol>DXCM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001760581</rptOwnerCik>
            <rptOwnerName>Malady Kyle</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>6340 SEQUENCE DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN DIEGO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92121</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-05-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5192</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>23334</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The RSU Award was granted on May 8, 2025 and 100% of the RSU Award will vest on the earlier of the one year anniversary of the grant date or the date of DexCom, Inc.'s 2026 Annual Meeting of Stockholders. Each share is represented by a restricted stock unit (RSU) that represents a contingent right to receive one share of DexCom, Inc. Common Stock upon settlement.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Jereme M. Sylvain, as Attorney-in-Fact for Kyle Malady</signatureName>
        <signatureDate>2025-05-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
