The prevalence of obsessive-compulsive disorder was measured in five US communities among more than 18,500 persons in residential settings as part of the National Institute of Mental Health (Bethesda, Md)--sponsored Epidemiologic Catchment Area program. Lifetime prevalence rates ranged from 1.9% to 3.3% across the five Epidemiologic Catchment Area sites for obsessive-compulsive disorder diagnosed without DSM-III exclusions and 1.2% to 2.4% with such exclusions. These rates are about 25 to 60 times greater than had been estimated on the basis of previous studies of clinical populations.