The relationship between obsessive-compulsive disorder (OCD) and putative obsessive-compulsive (OC) spectrum disorders is unclear. This study investigates the prevalence of putative OC spectrum disorders in OCD subjects in a controlled clinical design. The putative OC spectrum disorders studied included somatoform disorders (body dysmorphic disorder [BDD] and hypochondriasis), eating disorders, tic disorders (e.g., Tourette's syndrome [TS]), and impulse control disorders (e.g., trichotillomania). Only those disorders that are commonly noted to be possibly related to OCD are studied. Included in this study were 231 subjects with a diagnosis of OCD according to DSM-IV criteria and 200 controls who were not screened for psychiatric morbidity. The subjects and controls were assessed in detail by extensive clinical and semistructured interviews by expert clinical psychiatrists. The lifetime diagnoses were made by consensus of two psychiatrists. Prevalence of tic disorders, hypochondriasis, BDD, and trichotillomania was significantly greater in OCD subjects compared to controls. However, the prevalence of sexual compulsions, pathological gambling, eating disorders, and depersonalization disorder was not greater in the OCD subjects compared to controls. The findings of this comorbidity study suggest that tic disorders, hypochondriasis, BDD, and trichotillomania are perhaps part of the OC spectrum disorders. There is a need to evaluate evidence from other sources such as epidemiological, neurobiological, and family studies to further our understanding of the concept of OC spectrum disorders.