To investigate the need for hormonal treatment in patients with functional ovarian cysts (FOC), the efficacy of this treatment was evaluated in a retrospective and also in a randomised prospective study. By retrospective analyses the resolution of FOC with a mean diameter larger than 2.0 cm at the beginning of a cycle was determined in 113 patients (31.6 +/- 4.6 years). Fifty-seven women received an oral contraceptive (ethinylestradiol 50 micrograms/d for 7 days, ethinylestradiol 50 micrograms and desogestrel 125 micrograms/d for 15 days), the others had no therapy. In a second study 59 patients (32.3 +/- 4.6 years) were randomised to receive a combination of ethinylestradiol 50 micrograms and levonorgestrel 250 micrograms/d for 21 days (Group 1, n = 24), or lynestrenol 10 mg/d continuously (Group 2, n = 14) or a third group (Group 3, n = 21) without treatment. In both studies no differences were found between those patients who had hormonal treatment and those who had not. The prospective study revealed that spontaneously appearing FOC and FOC evolving after ovulation induction during the cycle prior to study enrolment, resolved equally well within 12 weeks independent of contraceptive or gestagen treatment. FOC persisted in only one woman (group 2) who had a surgically proven endometrioma. In conclusion, hormonal treatment does not produce regression of FOC in women of reproductive age.