<SEC-DOCUMENT>0000937556-17-000196.txt : 20170821
<SEC-HEADER>0000937556-17-000196.hdr.sgml : 20170821
<ACCEPTANCE-DATETIME>20170821162838
ACCESSION NUMBER:		0000937556-17-000196
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20170817
FILED AS OF DATE:		20170821
DATE AS OF CHANGE:		20170821

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FITCH SANFORD
		CENTRAL INDEX KEY:			0001198927

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-33642
		FILM NUMBER:		171043382

	MAIL ADDRESS:	
		STREET 1:		1212 TERRA BELLA AVENUE
		CITY:			MOUNTAIN VIEW
		STATE:			CA
		ZIP:			94043

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MASIMO CORP
		CENTRAL INDEX KEY:			0000937556
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTROMEDICAL & ELECTROTHERAPEUTIC APPARATUS [3845]
		IRS NUMBER:				330368882
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		52 DISCOVERY
		CITY:			IRVINE
		STATE:			CA
		ZIP:			92618
		BUSINESS PHONE:		949-297-7000

	MAIL ADDRESS:	
		STREET 1:		52 DISCOVERY
		CITY:			IRVINE
		STATE:			CA
		ZIP:			92618
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_150334730443859.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-08-17</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000937556</issuerCik>
        <issuerName>MASIMO CORP</issuerName>
        <issuerTradingSymbol>MASI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001198927</rptOwnerCik>
            <rptOwnerName>FITCH SANFORD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MASIMO CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>52 DISCOVERY</rptOwnerStreet2>
            <rptOwnerCity>IRVINE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92618</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-08-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>11000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>87.25</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>72249</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person contributed shares of the Issuer's common stock to an exchange fund in exchange for shares of the exchange fund. The shares of the Issuer's common stock were valued at $87.25 per share, the NASDAQ closing price on August 17,2017, for the purpose of determining the number of shares of the exchange fund issuable to the Reporting Person.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ David J. Van Ramshorst, Attorney-In-Fact</signatureName>
        <signatureDate>2017-08-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
