Forty-seven patients with nephrotic syndrome were prospectively studied for renal vein (RVT) and inferior vena caval (IVCT) thrombosis with dynamic CT. Renal venography and inferior vena cavography was performed on the 12 patients with and on 5 of the patients without CT evidence of thrombosis. Dynamic CT revealed thrombi in 12 of 47 (26%) of the cases (RVT in 8, IVCT in 5); all were confirmed by venography. In one of the cases with RVT, a thrombus in a superior branch of the left renal vein was revealed by venography but not by CT. Venography was normal in all five patients evaluated with normal dynamic CT. We believe that dynamic CT can be used to effectively examine patients with suspected RVT.