Endometriosis is a biologically benign albeit aggressive pathology marked by high local recurrences. Ureteral involvement accounts for only a minority of cases (0.1-0.4%) with often non-specific symptoms at clinical presentation and difficult preoperative diagnosis. Thirteen cases of severe ureteral endometriosis (i.e. causing significant obstruction to the urinary flow) were observed and surgically treated, out of 17 ureteral units affected (three cases of bilateral involvement, one case of complete pyeloureteral duplicity). The initial symptomatology was acute and related to ureteral obstruction in eight cases, silent and non-specific in the other five; a presumptive diagnosis was made only for the seven patients (53.9%) with a positive medical history for pelvic (and in two cases also ureteral) endometriosis. Preoperative drainage of urine proved necessary for eight patients due to the complete functional exclusion of the excretory axis. One patient (7.7%) underwent nephrectomy due to renal atrophy. Segmental ureteral resection and termino-terminal anastomosis were performed in two patients, while seven patients underwent segmental ureterectomy and ureterocystoneostomy, with bladder psoas hitching in four cases and vesical flap according to Casati-Boari in one case. All three cases of bilateral involvement were treated by bilateral segmental ureterectomy and trans-uretero-uretero-cystoneostomy with bladder psoas hitching. Following histological examination, all patients were diagnosed with active ureteral endometriosis, which was found to be intrinsic in five cases (38.5%) and extrinsic in the other eight. One of the two patients that had undergone ureterectomy and termino-terminal anastomosis had to undergo ureteral resection and ureterocystoneostomy 22 months later due to relapsing endometriosis-induced stenosis. Conversely, no ureteral endometriosis relapses occurred in the remaining 12 patients within the mean follow-up time of 41.1 months (range 6-91). Ureteral endometriosis is marked by non-specific symptoms, making preoperative diagnosis often difficult. Therefore, an ultrasound or urographic examination of the urinary tract in case of pelvic endometriosis is absolutely essential. In our experience, terminal ureterectomy with ureterocystoneostomy has provided long-term favourable results as extended ureteral resection can be performed and continuity of the urinary tract can be restored without resorting to the distal pelvic ureter, which is often affected by the disease besides being more subject to relapses.