At 8 years old, information on the boys' problem behaviors was obtained from their parents, teachers, and self-reports of the children themselves. At a 10-15-year follow-up, information on the sample's psychiatric disorders in early adulthood was obtained from Finland's national military register for the years 1999 and 2004. The register showed that 10.4 percent of the men had a psychiatric disorder in early adulthood. The problem behaviors reported by the boys' parents, teachers, and the boys' themselves at age 8 were clearly linked to the psychiatric disorders of early adulthood. Conduct symptoms at age 8 independently predicted substance abuse, antisocial personality, and psychotic disorders in early adulthood. Childhood depressive symptoms, poor school performance, and living in a nonintact family had an independent predictive association with antisocial personality and depressive disorders in early adulthood. Parent-reported emotional symptoms and self-reported psychosomatic symptoms independently predicted anxiety disorders in early adulthood. Approximately one-third of the boys who had used mental health services at age 8 had a psychiatric disorder in early adulthood. Among these service users, conduct and hyperkinetic symptoms predicted psychiatric disorders in early adulthood. The findings indicate the importance of childhood screening to identify and treat those behaviors and symptoms that, if left untreated, are likely to evolve into psychiatric disorders in early adulthood. 3 tables and 36 references