OBJECTIVE To perform criterion validation of the Key Question in Portuguese for screening at-risk alcohol use among users of Primary Healthcare services. METHOD This is a psychometric study conducted with users of a Primary Healthcare service located in the city of São Paulo, Brazil. Participants responded to the Key Question which was applied in conjunction with the Alcohol Use Disorders Identification Test-C for concurrent validation and measurement of psychometric properties. RESULTS The

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... le consisted of 518 users. The Key Question presented 59% specificity and 99% sensitivity with respect to the Alcohol Use Disorders Identification Test-C in the general population. The accuracy was 81% in relation to this instrument. There was no influence of sociodemographic variables such as gender on the psychometric properties of the Key Question. CONCLUSION The results indicate that the Key Question in Portuguese presented satisfactory psychometric qualities and suggest that its Portuguese version is as efficient for screening at-risk alcohol use as its reference standard, which subsidizes its use in Primary Healthcare.