The efficacy and safety of a new, low-dose, 21-day combination oral contraceptive containing 100 micrograms of levonorgestrel and 20 micrograms of ethinyl estradiol were evaluated in an open-label, multicenter trial. A total of 1477 subjects were enrolled and had 7870 cycles of exposure as of the data cutoff of this interim report. Of these, 792 subjects had completed six cycles of treatment. A total of five pregnancies occurred during treatment during 7720 efficacy cycles, for a Pearl index of 0.84. To date, 415 (28%) subjects have been withdrawn from the study for any reason, including 131 (9%) due to adverse events. The cumulative life table pregnancy rate was 0.0041 per woman entering the sixth cycle. Breakthrough bleeding alone occurred in 4.3% of the cycles and breakthrough bleeding and spotting occurred together during 11% of the cycles. Of the cycles evaluable, 2.6% were amenorrheic. The most commonly reported adverse events in this trial considered at least possibly drug related were headache (14%) and metrorrhagia (8%). This formulation provides contraceptive efficacy similar to higher-dose oral contraceptives, while maintaining a safety and common OC side effect profile that is consistent with prior years of reported use with levonorgestrel-containing products.