Background: Little is known about changes in the prevalence of psychiatric disorders between childhood and adolescence, and adolescence and adulthood. Methods: We reviewed papers reporting prevalence rates of psychiatric disorders separately for childhood, adolescence, and early adulthood. Both longitudinal and cross-sectional papers published in the past 15 years were included. Results: About one adolescent in five has a psychiatric disorder. From childhood to adolescence there is an increase in rates of depression, panic disorder, agoraphobia, and substance use disorders (SUD), and a decrease in separation anxiety disorder (SAD) and attention-deficit hyperactivity disorder (ADHD). From adolescence to early adulthood there is a further increase in panic disorder, agoraphobia, and SUD, and a further decrease in SAD and ADHD. Other phobias and disruptive behavior disorders also fall. Conclusions: Further study of changes in rates of disorder across developmental stages could inform etiological research and guide interventions.