<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>5</documentType><periodOfReport>2003-06-30</periodOfReport>
    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0001042064</issuerCik>
        <issuerName>NORTHWEST BANCORP INC</issuerName>
        <issuerTradingSymbol>NWSB</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001186992</rptOwnerCik>
            <rptOwnerName>KING A PAUL</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>102 STEPHANY ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FAIRVIEW,</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>16415</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>2146</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1780</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>Revocable Trust</value></natureOfOwnership></ownershipNature></nonDerivativeHolding></nonDerivativeTable><derivativeTable><derivativeHolding><securityTitle><value>Option Plan (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>9.78</value></conversionOrExercisePrice><exerciseDate><value>2001-10-18</value></exerciseDate><expirationDate><value>2011-10-18</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Northwest Bancorp, Inc.</value></underlyingSecurityTitle><underlyingSecurityShares><value>10000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>10000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Option Plan (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>9.78</value></conversionOrExercisePrice><exerciseDate><value>2001-10-18</value></exerciseDate><expirationDate><value>2011-10-18</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Northwest Bancorp, Inc.</value></underlyingSecurityTitle><underlyingSecurityShares><value>2000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>2000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding></derivativeTable><footnotes/><remarks/><ownerSignature><signatureName>A. Paul King</signatureName><signatureDate>2003-08-14</signatureDate></ownerSignature></ownershipDocument>

