OBJECTIVE: Psychotic experiences affect more than 10% of children and often co-occur with nonpsychotic mental disorders. However, longitudinal studies of the outcome of psychotic experiences based on unbiased information on mental health service use and psychotropic medications are scarce. The authors investigated whether psychotic experiences at ages 11-12 predicted a psychiatric diagnosis or treatment with psychotropic medications by ages 16-17. METHODS: In a longitudinal register-based follow-up study of the Copenhagen Child Cohort 2000, a total of 1,632 children ages 11-12 were assessed for psychotic experiences in face-to-face interviews. The children were also assessed for mental disorders and IQ. National registries provided information on perinatal and sociodemographic characteristics, on psychiatric disorders diagnosed at child and adolescent mental health services, and on prescribed psychotropic medications through ages 16-17. RESULTS: Among children who had not been previously diagnosed, and after adjustment for sociodemographic and perinatal adversities and IQ, psychotic experiences at ages 11-12 predicted receiving a psychiatric diagnosis in child and adolescent mental health services before ages 16-17 (adjusted hazard ratio=3.13, 95% CI=1.93, 5.07). The risk was increased if the child met criteria for a co-occurring mental disorder (not diagnosed in mental health settings) at baseline compared with no psychotic experiences or diagnosis at baseline (adjusted hazard ratio=7.85, 95% CI=3.94, 15.63), but having psychotic experiences alone still marked a significantly increased risk of later psychiatric diagnoses (adjusted hazard ratio=2.76, 95% CI=1.48, 5.13). Similar patterns were found for treatment with psychotropic medications. CONCLUSIONS: Psychotic experiences in childhood predict mental health service use and use of psychotropic medications during adolescence. The study findings provide strong evidence that psychotic experiences in preadolescence index a transdiagnostic vulnerability for diagnosed psychopathology in adolescence.