OBJECTIVE Substituting low-dose ethinyl estradiol (EE) for the hormone-free interval in combined oral contraceptives (COCs) may enhance ovarian suppression and improve tolerability. This noncomparative phase 3 study evaluated the efficacy and safety of a 21/7-active COC regimen including 21days of desogestrel (DSG)/EE followed by 7days of EE. METHODS This multicenter, open-label, phase 3, single-arm study enrolled sexually active women aged 18-40years at risk for pregnancy. Women received up to 1year, or 13 consecutive 28-day cycles, of DSG 150mcg/EE 20mcg for 21days and EE 10mcg alone for 7days. Participants kept diaries to record compliance, bleeding/spotting and other contraceptive use. Efficacy was measured using the Pearl Index (PI) and life-table approach. Safety and tolerability were assessed primarily through reported adverse events (AEs). RESULTS A total of 2858 women enrolled and 1680 completed the study. Forty-six pregnancies in 2401 women aged 18-35years occurred after COC initiation and up to 7days after last DSG/EE or EE-only tablet was taken. When cycles in which another contraceptive method was used were excluded, the PI was 2.68 [95% confidence interval (CI), 1.96-3.57]. The cumulative pregnancy rate after 1year of treatment was 2.47% (95% CI, 1.85-3.29) for all users aged 18-35years. When only cycles during which women considered compliant were included, the PI was 2.00 (95% CI, 1.39-2.80). AEs were similar to those seen with other oral contraceptives. CONCLUSIONS This 21/7-active DSG/EE COC with 7days of low-dose EE was efficacious and well tolerated for pregnancy prevention. CONCLUSIONS This phase 3 open-label study demonstrated that a 21/7-active COC regimen including 21days of DSG 150mcg/EE 20mcg and 7days of EE 10mcg was efficacious and well tolerated for pregnancy prevention.