Abstract Developmental aspects of psychiatric disorders may be inferred from patterns of age differences in prevalence. Age-specific prevalences are provided for nine disorders in a general population sample of ages 10–20. Age and gender patterns for several disorders suggest developmental stage-associated risks. These include oppositional disorder in both genders and conduct disorder and major depression in girls. Major depression shows a pattern suggestive of a role for the onset of puberty. The prevalence of one or more disorders did not differ by age or gender. However, the pattern of specific diagnoses varied greatly by both age and gender.