Study Objective: To evaluate the effects of vasopressin injection technique in laparoscopic cystectomy on ovarian reserve in patients with bilateral endometriomas. Design: Randomized prospective study (Canadian Task Force classification I). Setting: University hospital. Patients: Eighty-six women with bilateral endometriomas. Interventions: Laparoscopic cystectomy of bilateral endometriomas was performed using different techniques including laparoscopic cystectomy by stripping without injection (control group), laparoscopic cystectomy by stripping with injection of saline solution (saline group), and laparoscopic cystectomy by stripping with vasopressin injection technique (VIT group). Measurements and Main Results: The number of coagulation events on the ovarian cortex for hemostasis was counted in different groups, and the thickness of ovarian tissues removed was measured. The basal follicle-stimulating hormone (FSH) level was determined before surgery and at 3-, 6-, and 12-month follow-up after laparoscopic cystectomy in the different groups. In the saline group, fewer coagulation events were required to achieve hemostasis, less ovarian tissues were removed, and lower preoperative FSH levels were detected than in the control group (p < .01). In the VIT group, even fewer coagulation events (p < .01) and lower preoperative FSH levels (p < .01) were detected than in the saline group. There was no significant difference in the thickness of ovarian tissues removed in the 2 groups (p > .05). Basal FSH levels were significantly different before and after surgery in the control and saline groups (p <.01) but not in the VIT group (p > .05). Conclusion: Vasopressin injection is an ideal procedure to reduce damage from usual laparoscopic cystectomy of bilateral ovarian endometriomas to protect ovarian reserve.(c) 2014 AAGL. All rights reserved.