In a large meta-analysis, the prevalence of depression was twice as common in adolescents (5.7%) than children (2.8%). The 2:1 female to male ratio of depression seen in adults becomes apparent from the age of 12 years. Three quarters of children aged 3-17 years with depression also have anxiety, and almost half have associated behaviour problems. Depression should be treated by child and adolescent mental health services unless the episode is mild and of < 2-3 months’ duration.