In the period 1988-1990 this prospective study of 33 women with moderate or severe endometriosis who underwent laparoscopy for infertility and/or chronic pelvic pain, was conducted to evaluate the efficacy of aspirating endometriotic cysts followed by administration of a gonadotropin releasing hormone (GnRH) agonist in reducing the size of ovarian endometriomas. The cysts (mean diameter, 4.5 cm; range, 2-7; unilateral, 21 cases; bilateral, 12 cases) were punctured, aspirated, washed and emptied completely. After laparoscopy, 15 subjects received goserelin administered as a 28-day subcutaneous depot for three months, whereas 18 patients undergoing simple observation constituted internal controls. Ultrasound scans were performed before and at one, three and six months after laparoscopy. One case and three controls requested surgery between the four- and five-month follow-up scans and did not complete the study. All the other women had recurrent cysts at the six-month scan. There were no significant differences in mean endometrioma diameter between the two groups at any observation time nor between prelaparoscopic and six-month ultrasound examinations within each treatment group. We conclude that aspiration and washing of endometriotic cysts, combined with postoperative administration of GnRH agonists or not, is ineffective.