OBJECTIVE: The authors sought to determine the frequency of DSM-III personality disorders in subjects with obsessive-compulsive disorder, well comparison subjects, and their first-degree relatives. METHOD: Thirty-two subjects with obsessive-compulsive disorder and 33 age- (within 5 years) and gender-matched well comparison subjects were assessed with the Structured Interview for DSM-III Personality Disorder and several self-report instruments. Their first-degree relatives were assessed in a blind manner with the same instruments. RESULTS: Subjects with obsessive-compulsive disorder were more likely than well comparison subjects to have a personality disorder, but compulsive personality was not the most frequent. No significant differences were found in the prevalence of personality disorders among first-degree relatives, including compulsive personality, or in obsessional, hysterical, or oral character traits. CONCLUSIONS: Personality disorders are highly prevalent among patients with obsessive-compulsive disorder, but the data do not support a relationship between obsessive- compulsive disorder and compulsive personality.