With psychopathology rising during adolescence and evidence suggesting that the adult mental health burden is often due to disorders beginning in youth, it is important to investigate the epidemiology of adolescent mental disorders. We analyzed data gathered at ages 11 (baseline) and 19 of the population-based Dutch TRAILS study. At baseline we administered the Achenbach measures (CBCL, YSR) and at age 19 WHO's Composite International Diagnostic Interview (CIDI 3.0) to 1,584 youths. Lifetime, 12-month, and 30-day prevalences of any CIDI-DSM-IV disorder were 45%, 31%, and 15%, respectively. Half were severe. Anxiety disorders were most common but least severe whereas mood and behavior disorders were less prevalent but more severe. Disorders persisted, mostly by recurrence in mood disorders and chronicity in anxiety disorders. Median onset age varied substantially across disorders. Having one disorder increased subjects' risk of developing another disorder. We found substantial homotypic and heterotypic continuity. High problem levels at age 11 were modest precursors of incident adolescent disorders. Non-intact families and low maternal education predicted externalizing disorders. Most morbidity concentrated in 5% to 10% of the sample, experiencing 34% to 55% of all severe lifetime disorders. They seem to suffer from triple bad luck. At late adolescence, 22% of youths have experienced a severe episode and 23% only mild episodes. This psychopathology is rather persistent, mostly due to recurrence, showing both monotypic and heterotypic continuity. Family context affected externalizing disorders most. The burden of mental illness concentrates in 5% of the adolescent population.