3258 randomly selected adult household residents of Edmonton were interviewed by trained lay interviewers using the Diagnostic Interview Schedule (DIS). One of the diagnostic categories studied was obsessive-compulsive disorder (OCD). The lifetime and six month prevalence rates of OCD were 2.9% and 1.6% respectively. The morbidity risk, was equal in males and females at 5.4%. The peak age of risk of onset for both sexes was from the ages of 10 to 19 and, closely followed by the decade 20-29. Obsessions were found to be more frequently experienced than compulsions. Having a lifetime diagnosis of OCD is associated with an increased likelihood of developing depression, alcohol abuse, drug abuse, phobic disorders, and antisocial personality disorder. The significance of these findings is discussed for clinical practice.