Results of medical treatment with gestrinone are evaluated in 29 women with minimal (10), mild (9) and moderate (7) endometriosis. After a diagnostic laparoscopy, patients started gestrinone 2.5 mg/day 2 times a week per 6 months. Clinical evaluations and blood samples were performed at the end of the ist, 3rd and 6th month of treatment. A second look laparoscopy, in 26 out of the 29 patients, was performed within a month after discontinuation of the drug. Nineteen patients (73.1%) showed a diminishing in endometriosis score. Moreover, 2 of them presented with a normal pelvis at the time of the 2nd laparoscopy. Overall post treatment scores were significantly lower than pre treatment scores (6.1 +/- 6.9 versus 11.3 +/- 10.2 respectively, p < 0.025). Nineteen out of the 26 patients had amenorrhea, most of them (18) since the second month of treatment. Nineteen patients presented with dysmenorrhea at the beginning of the treatment and in 13 of them it disappeared during the first 3 months of the drug. Reversible elevation in serum transaminases was observed in 4 patients. Red blood cells count and platelet concentration increased at the end of the treatment. A clear pituitary suppression to basal levels was seen. No significant changes on androgen levels were appreciated. Seven patients achieved a spontaneous pregnancy, out of 22 that desired fertility (31.8%), all of them were clinical pregnancies.