PIP: A systematic study was undertaken in order to evaluate the consequences of missing oral contraceptives (OCs) at different times in the cycle. 39 young, healthy, normally menstruating patients were voluntarily enrolled in this study and all were given Cilest (ethinyl estradiol 35 mcg + norgestimate 250 mcg, Cilag, France) for 21 days without any gaps. Then, after a 7-day interval, they were prescribed 1 (group 1), 2 (group 2), 3 (group 3), or 4 (group 4) days of OC misses. These occurred on day 1 (class a), day 6 (class b), day 12 (class c), or day 18 (class d) of a 21 day Cilest cycle. In addition, supplementary contraceptive measures were recommended to those participating. With 47 cycles examined, 5 patients had no miss prescribed and this group served as the controls. Ovarian function was evaluated with daily estrogen monitoring (E1 + E2 enzymatic dosage, Bio Merieux, France) and ultrasound examination. When necessary, due to a significant estrogen increase or follicular growth detected on ultrasound, progesterone and LH were measured. 9 patients showed a follicular image on ultrasound. 4 patients (1 control, 3 others ) had a significant increase in estrogens and 2 others had no secretions. All the others had no manifestation of restoration of ovarian function. None of the 9 patients had a normal ovulation (no LH surge or increase in progesterone). Blockage of ovarian function by OCs remains efficient even after several days of OC missing. (author's modified)