Renal cell carcinoma with extended tumor thrombi densely adherent to the vena caval wall sometimes requires vena caval resection. If the tumor is on the right side and the collateral veins of the left renal vein are abundant, vena caval reconstruction may not be required. We recently performed radical nephrectomy and vena caval resection on 2 right renal cell carcinoma patients. To decide the necessity of vena caval reconstruction, left renal vein pressure was measured before and after clamping of the vena cava. In case 1, because the pressure was elevated from 21 cmH2O, to 61 cmH2O, total replacement with Gore-Tex graft was performed. In case 2, because the pressure change was from 22 cmH2O to 23 cmH2O, reconstruction was not performed. The most important test to decide the necessity of vena caval reconstruction is thought to be the change of renal venous pressure before and after clamping of the vena cava.