In a ten-year prospective study, mortality among psychiatric outpatients under age 40 was investigated in a sample of 322 Belgian patients who first visited a community mental health center in a district of Brussels between 1970 and 1973. Fifteen of the patients died before age 40. Compared with 15 matched controls from the group of living patients, the deceased patients had a higher incidence of concurrent physical illness and changed residence less frequently. The standardized mortality ratio for male patients in the study was 5.05 times greater than expected for a sample of the general population of Belgium, and for women it was 5.63 times greater. Not all of the excess mortality could be attributed to suicide. Results confirmed previous findings of excess mortality due to natural causes in this population and of the greater incidence of mortality during the first years of treatment.