The safety and efficacy of sertraline versus placebo were examined in a group of nondepressed outpatients with obsessive-compulsive disorder (OCD). Patients with moderate-to-severe OCD were recruited at 10 sites. After a 1-week placebo lead-in, patients were treated in a double-blind fashion for 12 weeks with sertraline or placebo. Sertraline was administered at a starting dose of 50 mg/day, with flexible titration up to 200 mg/day. The efficacy measures were the Yale-Brown Obsessive Compulsive Scale (Y-BOCS), the National Institute of Mental Health Global Obsessive Compulsive Scale (NIMH), and the Clinical Global Impression Scale (CGI) Severity of Illness and Improvement subscales. One hundred sixty-seven patients were randomly assigned and received at least one dose of double-blind medication: 86 received sertraline and 81 received placebo. All efficacy measures showed significantly greater improvement in the sertraline group from the end of week 8 until the end of week 12. Significantly greater improvement (p < 0.05) in the sertraline group first became apparent by the end of week 3 on the Y-BOCS and the CGI Improvement scale, and by the end of weeks 6 and 8, respectively, on the NIMH and CGI Severity scale. Sertraline was well tolerated, without serious adverse effects. In conclusion, sertraline was safe and effective in the treatment of patients with OCD.