OBJECTIVE To assess the contraceptive efficacy, cycle control and acceptability of two monophasic oral contraceptives containing either 30 micrograms ethinylestradiol plus 150 micrograms desogestrel or 30 micrograms ethinylestradiol plus 75 micrograms gestodene. METHODS In a randomized, open-label, six-cycle, group-comparative, multicenter study performed in Brazil, pregnancies, cycle-control parameters, incidence of side-effects and the presence and severity of acne vulgaris were assessed, and blood pressure and body weight were measured at pretreatment and after one, three and six cycles of oral contraceptive use. RESULTS Of the 595 women enrolled, 274 (86.7%) in the desogestrel/ethinylestradiol group and 227 (81.4%) in the gestodene/ethinylestradiol group completed the six cycles, providing data for 1753 and 1487 treatment cycles, respectively. Two pregnancies occurred, one of which (in the desogestrel/ethinylestradiol group) was attributed to user failure, whilst the other (in the gestodene/ethinylestradiol group) was thought to result from method failure. Cycle control was observed to be excellent; the incidences of irregular bleeding and minor side-effects were low in both groups and decreased after an initial increase in the first cycle. Pre-existing acne improved in both groups, whereas blood pressure and body weight remained essentially unchanged. CONCLUSIONS Both desogestrel/ethinylestradiol and gestodene/ethinylestradiol provide effective oral contraception with comparable cycle control and acceptability.