OBJECTIVE: To investigate the effect of two different laparoscopic methods on ovarian reserve in patients with ovarian endometriomas.DESIGN: Prospective, randomized clinical trial.SETTING: Endoscopy unit of a university hospital.PATIENT(S): Twenty women with endometriomas.INTERVENTION(S): Patients were randomly selected to undergo either laparoscopic cystectomy for endometrioma (group 1) or the "three-step procedure" (group 2). Before and 6 months after laparoscopy all patients were evaluated, and 12 months postoperatively they underwent ultrasound scan examination.MAIN OUTCOME MEASURE(S): The primary end point was ovarian reserve damage based on the alterations of anti-Müllerian hormone (AMH). Secondary end points were the changes of antral follicle count and serum concentration of FSH, LH, E(2), and inhibin B.RESULT(S): Mean serum AMH was reduced significantly from 3.9-2.9 ng/mL in group 1 compared with the reduction from 4.5-3.99 ng/mL in group 2.CONCLUSION(S): Ovarian reserve determined by AMH is less diminished after the three-step procedure compared with cystectomy of endometriomas.