Epidemiological research indicates that obsessive-compulsive disorder (OCD) still constitutes a major public health problem. To study the comorbidity of psychiatric disorders in OCD subjects in a non-Western community sample, 25,180 individuals were interviewed face-to-face at home according to DSM-IV for diagnosis of psychiatric disorders by 250 trained clinical psychologists. The subjects were predetermined with a randomized cluster sampling method among all families residing in Iran. From 444 individuals diagnosed as OCD, 157 (35.4%) developed at least one of the psychiatric disorders. The most common comorbid psychiatric disorders were major depressive disorder and simple phobia. Comorbidity of two or more additional psychiatric disorders in OCD individuals was rare. There was no difference between genders in the comorbidity of psychiatric disorders with OCD. Low comorbidity of psychiatric disorders with OCD shows that OCD tends to occur in isolated rather than as cluster problems in a clinical sample.