Objective:To evaluate the adequacy of laparoscopic ureterolysis as a primary treatment option for ureteral endometriosis. Design:Prospective collaborative cohort study. Setting:Gynecologic departments of three university hospitals. Patient(s):Women with ureteral endometriosis exhibiting moderate-to-severe hydronephrosis on preoperative intravenous pyelography. Intervention(s):Laparoscopic ureterolysis. Main Outcome Measure(s):Cure rate,disesase recurrence. Result(s):Thirty-three patients underwent laparoscopic ureterolysis during the study period. Bilateral involvement of ureters was found in 4 (12.1%) cases. In women with unilateral lesions the left ureter was more frequently affected (24/29 vs. 5/29). Ureteral involvement was associated with uterosacral ligaments endometriosis in 65.5%(22/34) of cases. No inadvertent ureteral injuries occurred during ureterolysis. A partial wall resection of the ureter was necessary in one case and a segmental ureteral resection with vescicopsoas hitch was required in a women with intrinsic ureteral endometriosis. The median (range) follow-up time was 16 months (range:3-53 months). Thirty-two patients (96.7%) had a patent ureter on the 3-month postoperative intravenous pyelography. The recurrence rate of ureteral lesions was 12.1%(4/33). Conclusion(s):Our findings suggest that a conservative laparoscopic approach is an effective treatment option in most patients with ureteral endometriosis exhibiting moderate-to-severe hydronephrosis. Objective: To evaluate the adequacy of laparoscopic ureterolysis as a primary treatment option for ureteral endometriosis. Design: Prospective collaborative cohort study. Setting: Gynecologic departments of three university hospitals. Patient (s): Women with ureteral endometriosis exhibiting moderate-to-severe hydronephrosis on preoperative intravenous pyelography. Intervention (s): Laparoscopic ureterolysis. Main Outcome Measure (s): Cure rate, disesase recurrence. Results (s): Thirty-three patients underwent laparoscopic ureterolysis during the study period. Bilateral involvement of ureters was found in In women with unilateral lesions the left ureter was more frequently affected (24/29 vs. 5/29). Ureteral involvement was associated with uterosacral ligaments endometriosis in 65.5% (22/34) of cases. No A partial wall resection of the ureter was necessary in one case and a segmental ureteral resection with vescicopsoas hit The median (range) follow-up time was 16 months (range: 3-53 months). Thirty-two patients (96.7%) had a patent ureter on the 3-month postoperative The recurrence rate of ureteral lesions was 12.1% (4/33). Conclusion (s): Our findings suggest that a conservative laparoscopic approach is an effective treatment option in most patients with ureteral endometriosis exhibiting moderate-to-severe hydronephrosis.