The World Health Organization's study on depressive disorders in different cultures began in 1972. Cohorts of depressed patients were identified in Basle, Montreal, Nagasaki, Teheran and Tokyo. The patients were assessed using standardized measures of social and clinical functioning. Ten-year follow-up data on clinical course, service contact, suicidal acts and social function outcomes were available for 439 (79%) patients. Over one-third (36%) were re-admitted at least once in the follow-up period, half of whom (18%) had very poor clinical outcome. Twenty-four per cent suffered severe social impairment for over half the follow-up period, and over one-fifth (21%) showed no full remissions. The best clinical course (one or two reasonably short episodes of depression with complete remission between episodes) was experienced twice as frequently in patients with a diagnosis of endogenous (65%) as in those diagnosed as suffering from psychogenic depression (29%). Among all patients, a fifth (22%) had at least one episode lasting for more than 1 year, and 10% had an episode lasting over 2 years during follow-up. Death by suicide occurred in 11% of patients, with a further 14% making unsuccessful suicide attempts.