A 32 year old lady presented with recurrent left flank pain for 4 weeks and chronic lower back pain. CT without contrast showed no stones and mild left hydronephrosis. CT of the spine suggested an inflammatory process at L5-S1 vertebra. The diagnosis was supported by a bone scan. Incidentally, the scan showed nonfunctioning left kidney. Diuretic renography confirmed poor perfusion and no excretion. A retrograde study showed narrowing of the ureter at the pelvic brim. Ureteroscopy showed a papillary mass in the lumen of the ureter from which multiple cold cup biopsies were taken. The pathology however was not conclusive. A robotic nephroureterectomy was carried out. Definitive pathology showed intrinsic endometriosis of the ureter. We conclude that endometriosis should be considered in the differential diagnosis of unexplained ureteric obstruction and ureteric lumen filling defects in young women.