To evaluate the need for maintenance drug therapy in patients with obsessive-compulsive disorder, the authors assessed 21 patients with obsessive-compulsive disorder who manifested sustained improvement during 5 to 27 months of clomipramine treatment and who agreed to participate in a double-blind discontinuation study. Of 18 patients who completed the study, 16 had substantial recurrence of obsessive-compulsive symptoms by the end of the 7-week placebo period. In addition, 11 had a significant increase in depressive symptoms. Treatment duration before discontinuation of clomipramine was not related to the frequency or severity of obsessive-compulsive or depressive symptom appearance. These findings suggest that prolonged drug treatment may be warranted for obsessive-compulsive disorder.