Objective: To describe the clinical characteristics and demographic details of a sample of patients with a principal diagnosis of obsessive compulsive disorder (OCD). Method: A retrospective review of fifty patients with DSM-III-R OCD referred to the Department of Behaviour Therapy at St. Patrick's Hospital, Dublin, Ireland between 1990 and 1991. Standard clinical ratings were made before and after treatment. Ratings used included the Maudsley Obsessive Compulsive Inventory (MOCI), the Fear Questionnaire (FQ), and the Yale-Brown obsessive compulsive score (YBOCS). Results: The male to female ratio was almost equal and the mean duration of illness was 6.1 (SD 11 years). OCD presented in isolation in a minority of cases (14%). A life time history of at least one other DSM-III-R axis I diagnosis, especially depression, was found in 72% of patients. Co-morbid Gilles de la Tourettes syndrome or epilepsy was rare. The majority of patients were on medication prior to presentation (78%). Levels of symptomatology were reduced in 91% of patients who completed treatment. Conclusions: Epidemiological research into the mass aspects of this disorder is required.