53歳女.両下肢の腫脹と乏尿を主訴に当院受診, CT上両側水腎症と両側腸骨動脈を取り囲む辺縁不整な軟部組織陰影を認めた, 腎後性腎不全に対し両側ダブルJカテーテル留置, 造影CTにて下大静脈及び左腸骨静脈内に血栓を認め, また下大静脈造影及びMRアンジオグラフィー(MRA)にて左腸骨静脈閉塞を認めた.中心静脈血栓を伴う特発性後腹膜線維症と診断し, 経口よりプレドニゾロン及びワーファリン投与開始した.投与1ヵ月後のCT及びMRAで血栓の消失を認め, 水腎症は改善, 再発を認めていないA 53-year-old female was hospitalized for evaluation of swelling in the bilateral lower extremities. A computed tomography (CT) scan of the abdomen revealed bilateral hydronephrosis and features consistent with retroperitoneal fibrosis. Transfemoral venography and magnetic resonance angiography (MRA) showed thrombosis of both the left common iliac vein and inferior vena cava, and filling of numerous collateral veins in the retroperitoneal area. A diagnosis of idiopathic retroperitoneal fibrosis with central venous thrombosis was made. Ureteral stenting, medication with corticosteroids and subsequent warfarin were started, resulting in marked improvement of renal function and the lower extremities. Diagnosis and follow-up of deep venous thrombosis can be aided by MRA. Administration of steroids with anticoagulation was considered to be successful in the case presenting with deep venous thrombosis caused by retroperitoneal fibrosis