Nineteen adolescent girls with oligomenorrhea were studied to evaluate the effect of oral contraceptives (OCs) on hormone profiles, and 19 adolescent girls with regular menstruations served as control subjects. Serum levels of luteinizing hormone and androgens were higher in the oligomenorrheic girls than in the regularly menstruating girls. During the OC treatment the hormone levels of the oligomenorrheic girls decreased, approaching those of the control subjects. During follow-up cycle immediately after stopping the OCs the hormone levels increased rapidly, but in the oligomenorrheic girls the levels of luteinizing hormone, androstenedione, total and free testosterone were still significantly lower at the end of the post-treatment cycle than during the luteal phase of the pre-treatment cycle. The frequency of ovulation decreased to the same magnitude as reported in adults after discontinuation of OCs. No post-pill amenorrhea existed in either group of adolescents.