This prospective, open, randomized study was conducted to compare the contraceptive reliability, cycle control, and tolerability of a 23-day regimen with 20 microg ethinyl estradiol (EE) and 75 microg gestodene (GSD) and a 21-day regimen with 20 microg EE and 150 microg desogestrel (DSG). Participants took either 23 tablets with active substances plus 5 placebo tablets (23-day EE/GSD) or 21 tablets with active substances followed by 7 days without pill-taking (21-day EE/DSG). Contraceptive efficacy, cycle control, and tolerability were evaluated over a period of seven cycles. Efficacy data gathered from 5967 treatment cycles (23-day EE/GSD: 2975 cycles; 21-day EE/DSG: 2992 cycles) were obtained from 890 participants (445 in each group). Both preparations proved to be effective contraceptives and provided good cycle control. No pregnancy during treatment was recorded. This resulted in a study Pearl Index of 0.0 for both treatments. For 23-day EE/GSD, 32.4% of participants reported at least one intracyclic bleeding episode during Cycles 2-4 (primary target) compared to 31.5% for 21-day EE/DSG. In the 23-day EE/GSD group, intracyclic bleeding episodes were reported by 48.8% of the participants in Cycle 1 but in only 15.1% in Cycle 7, and in the 21-day regimen group by 43.4% in Cycle 1 and only 14.2% in Cycle 7. Overall, intracyclic bleeding was reported in 20.9% of cycles for both treatments.A greater number of 23-day EE/GSD participants had shorter withdrawal bleeding periods than with 21-day EE/DSG. In significantly (p <0.0001) more cycles in the 23-day EE/GSD group participants reported withdrawal bleeding periods that lasted only 1-4 days compared to the 21-day EE/DSG group. For the majority of the treatment cycles, the median number of bleeding days in the 23-day EE/GSD group was 4 days and in the 21-day EE/DSG group 5 days. Both preparations were well tolerated and showed a similar adverse events pattern. The discontinuation rate because of adverse events was low (23-day EE/GSD: 6.1%; 21-day EE/DSG: 5.6%). No serious vascular adverse events were reported. More than 82% in the 23-day EE/GSD group and 79% in the 21-day EE/DSG group either lost more than 2 kg of weight or did not gain weight during the study. The treatment effect on blood pressure was negligible. There were no appreciable changes in mean laboratory values over the course of the study compared to baseline.