Objective: To assess the prevalence of psychotic symptoms among youths (14-25 years of age) with a childhood diagnosis of attention-deficit/hyperactivity disorder (ADHD) combined type. Method: Participants in the Multimodal Treatment Study of Children with ADHD (MTA) and a local normative comparison group (LNCG) were systematically assessed 6, 8, 10, 12, 14, and 16 years after the original enrollment at a mean age of 8.5 years. Trained research assistants administered a psychosis screener, and positive screens were referred to study clinicians to confirm or exclude psychosis. Possible associations between screening positive and alcohol or substance use were assessed. Results: Data were available from 509 MTA participants (88% of original MTA sample; mean age 25.1 years) and 276 LNCG participants (96% of original sample; mean age 24.6 years) at year 16. Twenty-six MTA participants (5%; 95% CI 3-7) and 11 LNCG participants (4%; 95% CI 2-6)screened positive for at least 1 psychotic symptom (p =.60). Most psychotic symptoms were transient. The prevalence of clinician-confirmed psychotic symptoms was 1.1% (95% CI 0.2-2.1) in the MTA group and 0.7% (0-1.7) in the LNCG (p =.72). Greater cannabis use was reported by those who screened positive (p<.05) and were confirmed positive (p<.01). Conclusion: There was no evidence that ADHD increased the risk for psychotic symptoms. In the ADHD and normative comparison groups, more frequent cannabis use was associated with a greater likelihood of experiencing psychotic symptoms, thus supporting the recommendation that youth should not use cannabis.