OBJECTIVES: To describe lifetime prevalence rates, course and comorbidity of obsessive-compulsive disorder (OCD), obsessive-compulsive syndromes (OCS) and OC-symptoms (OC-sx) up to age 41. METHODS: In the Zurich community cohort study 591 subjects were selected after screening at the age of 19 and studied prospectively by 6 interviews from 20 to 40; they represent 1599 subjects of the normal population. The diagnoses of OCD met DSM-IV criteria. Course was assessed by graphic illustrations and prospective data. RESULTS: The lifetime prevalence rate was 3.5 % for OCD (males 1.7%, females 5.4 %) and 8.7 % for OCS (males 9.9%, females 7.5 %). The onset of OC-sx was 18 years (median); and in 70% before age 20. OCD was treated in one third of cases, OCS in 6.1%. The course of symptoms was chronic in 60%,but OCD and OCS showed in most cases considerable improvements over time. OCD reduced quality of life mostly in the subject's psychological wellbeing and at work but to a considerable extent also in other social roles. Comorbidity was prominent with bipolar disorder, panic disorder and social phobia and also significant with bulimia, binge eating, generalized anxiety disorder and suicide attempts; there was no association with substance abuse/dependence. CONCLUSION: OCD and OCD are manifestations of a wide spectrum of severity with high prevalence and strong clinical validity. The long-term course is better than generally assumed.