Between January 1985 and November 1992, 12 patients with renal cell carcinoma involving the inferior vena cava were evaluated and treated at this hospital. In 4 of the 12 patients (33%), the tumors extended into the right atrium. These 4 patients underwent radical nephrectomy with tumor thrombus extraction. Of the 4 patients one had metastases to regional lymph nodes, but no patient had distant metastases. We used a cardiopulmonary bypass and a right atriotomy in all patients for the removal of thrombus under direct vision. We also performed in the intra-operative transesophageal ultrasonography for monitoring of intra-atrial thrombus. The average blood loss during operation was 10,430 ml. One of these patients died in the postoperative period and the other patient died from inferior vena caval emboli without long term sequelae. However, the remaining 2 patients of this group are free of disease, with a mean follow-up of 21 months. Although the numbers are small, these results suggest that patients with intra-atrial tumor thrombus had a worse prognosis than those with other types of vena cava tumor thrombus. One reason for this poor prognosis is due to the complicated surgical management and we believe that a complete removal of tumor thrombus and a complete vascular control are key points of this operation.