Vena caval extension of renal cell carcinoma occurs in 4 to 10 per cent of the patients and usually is considered a poor prognostic sign. To ascertain the true effect of vena caval extension on survival a retrospective analysis was done of 27 patients who had undergone radical nephrectomy and removal of vena caval thrombus between 1970 and 1980. An additional 46 cases were collected from series in the literature and composite statistics were compiled. Extension to the vena cava alone had a limited impact on prognosis (survival for 2 years - 81 per cent, 5 years - 53 per cent, median - 81 months). Capsular invasion negatively influenced survival (2-year survival 66 per cent). Disease in the regional lymph nodes had a much greater impact on survival with a 2-year survival rate of 35 per cent and no patient survived 5 years (median survival 24 months). Only 5 per cent of the patients with distant metastases survived 2 years and none survived 5 years (median survival 8.5 months). In conclusion, the prognosis of patients with vena caval tumor thrombus is influenced primarily by known adverse prognostic factors: capsular invasion, nodal disease and distant metastases. Aggressive surgery in patients with gross nodal involvement or distant metastases is unwarranted since it contributes nothing to survival and only 7 per cent of patients had significant signs or symptoms secondary to the vena caval thrombus itself. Patients with vena caval extension alone have a cure rate approaching that of patients with stage I renal carcinoma following radical nephrectomy and complete removal of the vena caval thrombus.