Background: An excess of androgen is believed to contribute to development of acne in some patients. Because oral contraceptives (OCs) may reduce the active androgen level, hormonal therapy with OCs has been used successfully to treat patients with acne, although this treatment has previously not been studied in placebo-controlled trials. Objective: Our purpose was to evaluate the efficacy of a triphasic, combination OC (ORTHO TRI-CYCLEN [Ortho-McNeil Pharmaceutical, Raritan, N.J.], norgestimate/ethinyl estradiol) compared with placebo in the treatment of moderate acne vulgaris. Methods: Two hundred fifty-seven healthy female subjects, 15 to 49 years of age with moderate acne vulgaris, were enrolled in a multicenter, randomized, double-blind, placebo-controlled clinical trial. Each month for 6 months, subjects received either 3 consecutive weeks of the OC (i.e., tablets containing a fixed dose of ethinyl estradiol [0.035 mg] and increasing doses of norgestimate [0.180 mg, 0.215 mg, 0.250 mg]) followed by 7 days of inactive drug or placebo (color-matched tablets). Efficacy was assessed by facial acne lesion counts, an investigator’s global assessment, a subject’s self-assessment, and an analysis of within-cycle variation (cycle 6) in lesion counts. Results: Of the 160 subjects in whom efficacy could be evaluated, the OC group showed a statistically significantly greater improvement than the placebo group for all primary efficacy measures. The mean decrease in inflammatory lesion count from baseline to cycle 6 was 11.8 (62.0%) versus 7.6 (38.6%) ( p = 0.0001), and the mean decrease in total lesion count was 29.1 (53.1%) versus 14.1 (26.8%) ( p = 0.0001) in the OC and placebo groups, respectively. In the investigator’s global assessment, 93.7% of the active treatment group versus 65.4% of the placebo group were rated as improved at the end of the study ( p < 0.001). Six of the seven secondary efficacy measures (total comedones, open comedones, closed comedones, papules, pustules, and the subject’s self-assessment of study treatment) were also significantly more favorable in the OC group compared with the placebo group. Conclusion: An OC containing 0.035 mg of ethinyl estradiol combined with the triphasic regimen of norgestimate is a safe and effective treatment of moderate acne vulgaris in women with no known contraindication to OC therapy. (J Am Acad Dermatol 1997;37:746-54.)