<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-06-18</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000911177</issuerCik>
        <issuerName>CASELLA WASTE SYSTEMS INC</issuerName>
        <issuerTradingSymbol>CWST</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001055352</rptOwnerCik>
            <rptOwnerName>CASELLA JOHN W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CASELLA WASTE SYSTEMS</rptOwnerStreet1>
            <rptOwnerStreet2>25 GREENS HILL LANE</rptOwnerStreet2>
            <rptOwnerCity>RUTLAND</rptOwnerCity>
            <rptOwnerState>VT</rptOwnerState>
            <rptOwnerZipCode>05701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>CEO</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable></nonDerivativeTable>
<derivativeTable><derivativeTransaction><securityTitle><value>Option</value>
</securityTitle>
<conversionOrExercisePrice><value>9.12</value>
</conversionOrExercisePrice>
<transactionDate><value>2003-06-18</value>
</transactionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>A</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>20000</value>
</transactionShares>
<transactionPricePerShare><value>9.12</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode><value>A</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<exerciseDate><footnoteId id="F1"></footnoteId>
</exerciseDate>
<expirationDate><value>2013-06-17</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>20000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>20000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeTransaction>
<derivativeTransaction><securityTitle><value>Option</value>
</securityTitle>
<conversionOrExercisePrice><value>9.12</value>
</conversionOrExercisePrice>
<transactionDate><value>2003-06-18</value>
</transactionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>A</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>10000</value>
</transactionShares>
<transactionPricePerShare><value>9.12</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode><value>A</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<exerciseDate><footnoteId id="F2"></footnoteId>
</exerciseDate>
<expirationDate><value>2013-06-17</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>10000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>10000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeTransaction>
</derivativeTable>
<footnotes><footnote id="F1">This option is immediately exercisable with respect to 10,000 of the shares granted and shall become exercisable with respect to the remaining 10,000 shares on June 18, 2004.</footnote>
<footnote id="F2">This option shall become fully exercisable on June 18, 2005.</footnote>
</footnotes>
<ownerSignature><signatureName>/s/ John W. Casella</signatureName>
<signatureDate>2003-09-29</signatureDate>
</ownerSignature>
</ownershipDocument>

