A case of left renal cell carcinoma with a tumor thrombus extending into the vena cava and the right atrium is reported. A 49-year-old female presented with a one month history of palpitation, dyspnea, and leg edema. CT-scanning and angiography revealed a left renal tumor with a tumor thrombus extending into the right atrium. Left nephrectomy and the removal of an intra-atrial tumor thrombus were performed under cardiopulmonary bypass. The postoperative course was unfavorable and the patient died on the 42nd day after the operation because of multiple organ failure in spite of repeated hemoperfusion. Operative procedure and prognosis of renal cell carcinoma with tumor thrombus extending into the right atrium are discussed.