A clinical study was performed with a new progestogen, desogestrel, in a 0.15 mg dose associated with 0.03 mg of ethinylestradiol and was administered cyclically during 21 days; 632 cycles were evaluated in 56 women. Side-effects were scarce and generally of a mild nature. Monthly bleeding was normal and present in all cycles. Patients with irregular cycles were normalized to 28/29 days. The intermenstrual bleeding (spotting) was an isolated event in 16 cycles. Mastalgia, the most frequent symptom, disappeared spontaneously in the majority of patients. In only 2 cases was it necessary to stop medication because of side-effects. The contraceptive effect was excellent; no pregnancies occurred. A progestative effect was evident in the cervical mucus and the endometrium. The patients who started treatment with acne improved noticeably. In the mild cases, acne disappeared completely. A discrete improvement in hirsutism was reported. The body-weight variation was not significant. Biochemical studies revealed an increase in HDL-C and a decrease in the ratio LDL-C/HDL-C. Cholesterol and triglycerides did not show variations, which could indicate a lesser cardiovascular risk.