Adult substance users are known to have above average rates of Attention Deficit–Hyperactivity Disorder (ADHD), but the psychometric properties of self-report measures of ADHD symptoms for adult substance users are unknown. Subjects (206 adults with a DSM-IV substance abuse disorder) were administered the Conners Adult ADHD Rating Scales (CAARS) upon enrolling in outpatient treatment. A factor structure similar to that reported for other populations was obtained and internal consistency reliabilities for the subscales and the overall index were high. Compared with CAARS norms, substance users scored significantly above average on all subscales as well as on the overall index. The CAARS may prove useful for measuring ADHD symptomatology among substance users, but additional reliability and validity evidence is needed. The CAARS should not be used by itself to diagnose individuals for ADHD.