We report a case of metastatic seminoma with direct invasion of the left renal vein. A tumor thrombus was found in the renal vein while the vena cava thrombosis proved to be a noncancerous blood clot developing as an extension of the tumor thrombus. Primary chemotherapy could not be completed because of thrombotic growth requiring surgical intervention. Although surgical specimens were free of viable tumor and two cycles of adjuvant chemotherapy were applied, the tumor relapsed in the area of renal vein invasion.