Idiopathic retroperitoneal fibrosis (RF) is a histologically benign, nonspecific inflammatory process of the fibroadipose tissue in the retroperitoneum with an unknown etiology. It may be complicated due to encasement and obstruction of the retroperitoneal structures. Tamoxifen has been known to be an effective agent in regression of desmoid tumors which include similar mesenchymal elements to those seen in RF. Herein, we reported a case of RF presented with ureteral obstruction and acute renal failure. The patient was successfully treated with tamoxifen.