Although hot spots on hepatic scintigrams have been reported in association with superior and inferior vena caval obstruction, these studies were not clinically correlated, and are hampered by the poor resolution of earlier scintillation cameras. In this report, a modern scintillation camera was used to study the formation of hot spots associated with superior and inferior vena caval obstruction. Moreover, radionuclide cavography was performed in 70 patients with superior vena caval (SVC) obstruction and in 95 patients with inferior vena caval (IVC) obstruction. As a result, 13 cases of hot spots in the liver were observed. In cases of SVC obstruction, hot spots were seen in the quadrate lobe, the medial segment, and the bare area of the liver. In IVC obstruction, a hot spot was seen in the quadrate lobe in all cases. In rare instances, in cases of both SVC and IVC obstruction, a hot spot was seen in the wide area. For these hot spots to develop, it appears necessary to have systemic-portal venous blood flow through the internal thoracic vein and the paraumbilical vein.