To evaluate the feasibility of cingulotomy as a treatment for patients with intractable obsessive-compulsive disorder, we evaluated the records of all 35 patients with this diagnosis who had undergone one or more such procedures at Massachusetts General Hospital, Boston, during the last 25 years. Retrospectively, all but two of these patients met DSM-III-R criteria for obsessive-compulsive disorder. Six patients were deceased; four by suicide. Questionnaires were sent to the remaining 27 patients with obsessive-compulsive disorder; 17 patients returned the questionnaire and another agreed to an interview without completing the forms. Sixteen of these 18 patients participated in a telephone interview, and patient reports were corroborated by an informant in 10 cases. Despite the presence of some side effects, such as easily controlled seizures (9%) and transient mania (6%), the results of this investigation support the use of cingulotomy as a potentially effective treatment for patients with severe and disabling obsessive-compulsive disorder. With the use of very conservative criteria, we estimated that at least 25% to 30% of the patients benefited substantially from this procedure. Similar results were found in a preliminary prospective study of four patients who recently underwent cingulotomy after state-of-the-art preoperative treatments had failed.