A 76-year-old woman presented with dull pain in left flank. Excretory urogram showed no function of left kidney. Retrograde pyelography, ultrasonography, computed tomography and magnetic resonance imaging demonstrated hydronephrosis of the left kidney and a mass lesion surrounding the ureter. The tumor was removed together with the upper region of the left ureter and kidney. The tumor was 5 x 3 x 2.5 cm in diameter and the pathological diagnosis was a leiomyosarcoma. Although recurrent tumor arose in the pelvis at 14 months after the operation, the patient has been in good general condition without showing any other evidence of recurrent lesion. This case may indicate the importance of early resection of retroperitoneal leiomyosarcoma.