Involvement of inferior vena cava (IVC) by tumor thrombus occurs in up to 10% of patients with nephroblastoma. Right atrial involvement by tumor thrombus is much less frequent. Four patients presenting with advanced nephroblastoma were diagnosed as having IVC involvement with tumor thrombus. Two of these patients had in addition thrombus extending up to the right atrium. All 4 patients were treated with preoperative chemotherapy (vincristine, actinomycin D, 4-epi-Adriamycin). Nephrectomy was subsequently performed without undue difficulty on all 4 patients. The intravascular tumor thrombus had completely cleared in all 4 patients and most of the primary renal tumor was necrotic. The results obtained with preoperative chemotherapy as given to these patients mediates strongly against difficult surgery being undertaken as primary treatment for such patients.