Sexual dysfunction, a frequently reported side effect of many antidepressants, may result in patient dissatisfaction and noncompliance with treatment regimens. This paper describes the results of the first placebo-controlled comparison of the efficacy, safety, and effects on sexual functioning of sustained-release bupropion (bupropion SR) and the selective serotonin reuptake inhibitor sertraline. This randomized, double-masked, double-dummy, parallel-group, multicenter trial enrolled 360 patients with moderate-to-severe recurrent major depression. Patients were treated with bupropion SR 150 to 400 mg/d, sertraline 50 to 200 mg/d, or placebo for up to 8 weeks. Patients' depression and sexual functioning were assessed at weekly or biweekly clinic visits; safety was assessed by regular monitoring of adverse events, vital signs, and body weight. Treatment groups were similar at baseline in terms of age, sex, and race, and most patients had a diagnosis of moderate uncomplicated depression. Patients treated with bupropion SR or sertraline showed similar improvements on all efficacy measures; both active treatments were superior to placebo in improving scores on all rating scales for depression at various time points. Significantly more patients treated with sertraline experienced orgasmic dysfunction throughout the study than did patients treated with bupropion SR or placebo (P < 0.001). Headache was the most frequently reported adverse event in all 3 treatment groups and occurred with similar frequency in each group (30% to 40%). Nausea (31%), diarrhea (26%), insomnia (18%), and somnolence (17%) occurred in significantly more patients in the sertraline group than in the bupropion SR group (18%, 7%, 13%, and 3%, respectively) and the placebo group (10%, 11%, 4%, and 6%, respectively). Dry mouth occurred more frequently with bupropion SR (19%) than with sertraline (14%) or placebo (12%), although the differences were not significant. Changes in vital signs were similar in all groups. Similar (small, but not statistically significant) decreases in mean body weight were seen in both the bupropion SR (-1.06 kg) and sertraline (-0.79 kg) groups, whereas the placebo group experienced a minor increase (0.21 kg). Although bupropion SR and sertraline were similarly well tolerated and effective in the treatment of depression, sertraline treatment was more often associated with sexual dysfunction and certain other adverse events compared with bupropion SR and placebo. Therefore, bupropion SR may be an appropriate choice as an antidepressant for the treatment of sexually active patients.