Research on the long-term outcome of mental disorders originating in childhood and adolescence is an important part of developmental psychopathology. After a brief sketch of relevant terms of outcome research, the first part of this review reports findings based on heterotypic cohort studies. The major second part of this review presents findings based on long-term outcome studies dealing with homotypic diagnostic groups. In particular, the review focuses on the course and prognosis of ADHD, anxiety disorders, depression, conduct disorders, eating disorders, autism spectrum disorders, schizophrenia, and selective mutism. Findings mainly support the vulnerability hypothesis regarding mental disorders with early manifestation in childhood and adolescence as frequent precursors of mental disorders in adulthood. The discussion focuses on the impact of early manifesting disorders in the frame of general mental morbidity and of the effect of interventions, which is not yet sufficiently discernible.