A 46-year-old woman, who had been treated with anti-arrhythmic drugs and digitalis for mitral stenosis and paroxysmal atrial fibrillation, suddenly developed severe abdominal pain and nausea. There was tenderness around right CVA. BUN and serum-creatinine were elevated, 57 mg/dl and 4.5 mg/dl respectively. She was in acute renal failure (ARF). WBC, GOT, GPT, LDH were also elevated. Abdominal ultrasonography showed normal-size right kidney (12 cm) and atrophic left kidney (8.5 cm). Selective right renal angiography revealed right renal arterial embolism, suggesting that ARF developed from right renal infarction complicated by left atrophic kidney. Renal scintigram using 99mTc-DTPA indicated non-function type left kidney. Because of the high risk of surgery, she received anticoagulant therapy. Fifteen days later, BUN and serum-creatinine returned to 14mg/dl, 2.2mg/dl, respectively.