The patient was a 49-year-old male with the chief complaint of right lower extremity edema. Ultrasonography showed a right hydronephrosis and a thickening of the right side of bladder wall. No bladder tumor was found by cystoscopy. The right renal pelvis and ureter were not visualized by drip infusion pyelography (DIP). Computed tomography (CT) demonstrated a soft tissue mass surrounding the bilateral common iliac artery and extending to thickened bladder wall. After the echo-guided needle biopsy, steroid therapy was performed under the diagnosis of the idiopathic retroperitoneal fibrosis. Prednisolone was administered for 10 weeks, resulting in the complete disappearance of thickening of the bladder wall.