A case of bilateral ureteral fibrosis is reported. The patient, a 32-year-old man, was admitted as a result of acute renal failure. Ultrasonography showed bilateral hydronephrosis, so that in-dwelling percutaneous nephrostomy tubes were immediately inserted in the bilateral kidneys. Since retrograde and antegrade pyelograms revealed bilateral midureteral stricture, idiopathic retroperitoneal fibrosis at first suspected, but no mass in the retroperitoneal space was found by a computed tomogram. An exploratory laparotomy showed no fibrous mass in the retroperitoneal space either, but that the wall of the ureter was thickened. Biopsy of the ureter led to a histological diagnosis of fibrosis. Since evidence of inflammation such as elevation of the erythrocyte sedimentation rate and cross-reacting protein was found, 50 mg of prednisolone has been administered every other day, with the result that inflammation is now under control. This report deals with specific ureteral fibrosis related to idiopathic systemic fibrosis and collagen disease.