Previous studies have shown that substance misuse in adolescence is associated with increased risks of hospitalizations for mental and physical disorders, convictions for crimes, poverty, and premature death from age 21 to 50. The present study examined 180 adolescent boys and girls who sought treatment for substance misuse in Sweden. The adolescents and their parents were assessed independently when the adolescents first contacted the clinic to diagnose mental disorders and collect information on maltreatment and antisocial behavior. Official criminal files were obtained. Five years later, 147 of the ex-clients again completed similar assessments. The objectives were (1) to document the prevalence of alcohol use disorders (AUD) and drug use disorders (DUD) in early adulthood; and (2) to identify family and individual factors measured in adolescence that predicted these disorders, after taking account of AUD and DUD in adolescence and treatment. Results showed that AUD, DUD, and AUD + DUD present in mid-adolescence were in most cases also present in early adulthood. Prediction models detected no positive effect of treatment in limiting persistence of these disorders. Thus, treatment-as-usual provided by the only psychiatric service for adolescents with substance misuse in a large urban center in Sweden failed to prevent the persistence of substance misuse. Despite extensive clinical assessments of the ex-clients and their parents, few factors assessed in mid-adolescence were associated with substance misuse disorders 5 years later. It may be that family and individual factors in early life promote the mental disorders that precede adolescent substance misuse.