ABSTRACTAge of onset of psychiatric disorders was determined from a random sample of 3, 258 household residents who were administered the DIS by trained lay interviewers. Onset was determined by the subject's recall of the age of the first symptom in those who met lifetime criteria for a diagnosis (DSM III without exclusions). The peak age of risk for most disorders was from the teens to 30 years, however a number of schizophrenics showed first symptoms before age 10. Few cases of any disorder had an onset in old age. The ages of onset are generally lower than those usually given from series of treated or hospitalized cases.