This study was undertaken to establish the frequency of membranous obstruction of the inferior vena cava in South Africa, to characterize the pathology of the lesion and to define its relationship to hepatocellular carcinoma. Over a 9-yr period 101 cases of membranous obstruction of the inferior vena cava into the right atrium was occluded in all cases in which it was examined, and two basic patterns of the abnormality in the hepatic portion of the inferior vena cava have been described. The histologic picture in the liver was a chronic congestive fibrosis. In 44 cases of congestive fibrosis, diagnosed from liver biopsy specimens from black patients over a 5-yr period, vena caval membranes were demonstrated on cavography in 38 (86.4%). Hepatocellular carcinoma developed in 48 of the 101 cases (47.5%), indicating the importance of this defect in the pathogenesis of hepatocellular carcinoma in South Africa.