Eleven patients with paroxysmal nocturnal hemoglobinuria were studied by serial liver imaging. This disease has a generalized thrombotic tendency, and progressive diffuse hepatic venous thrombosis has been emphasized in recent studies. Radionuclide imaging proved to be of great help in establishing the diagnosis of hepatic venous thrombosis and following the progress of the disease process. Abnormal patterns in hepatic venous occlusion include (a) enlargement of the liver (especially the right lobe), (b) extrahepatic localization of radionuclide, and (c) areas of decreased uptake in the distribution of the involved veins. These findings develop rapidly and are very characteristic in the clinical setting.