Key PointsQuestionWhat are the psychometric properties of a Substance Use Symptom Checklist used routinely in primary care among patients reporting high-risk cannabis and/or other drug use?FindingsIn this cross-sectional study of 23 304 positive screens for daily cannabis or any other drug use, the 11-item checklist provided scaled, unidimensional information on the presence and severity of substance use disorder. The checklist performed well across patient age, sex, race, and ethnicity.MeaningThe findings of this study support the use of the checklist in primary care as a tool to aid clinicians in eliciting patient symptoms, identifying a spectrum of substance use disorder severity, and clinical decision-making based on diagnostic criteria.