Budd-Chiari syndrome (BCS) was initially defined as a symptomatic occlusion of the hepatic veins, but subsequent reports on various obliterative changes that occur in the hepatic portion of the inferior vena cava (IVC) and hepatic vein orifices have resulted in a broadened and ambiguous definition. Membranous obstruction of the inferior vena cava has been regarded by many as a congenital vascular malformation, but its relation to the classical BCS has remained obscure. With modern imaging and recent histological study of new cases, membranous obstruction of the IVC is now considered to be a sequela to thrombosis. How to classify various forms of occlusion and stenosis of the IVC and hepatic vein ostia is a major challenge. In this review, we emphasize that primary hepatic vein thrombosis (classical Budd-Chiari) and an obliterative disease predominantly affecting the hepatic portion of the IVC, both of which account for most patients with venous outflow block, are clinically quite different. In the West, the former is more common than the latter, which constitutes the vast majority of cases of outflow block in developing countries such as Nepal, South Africa, China, and India. The latter is frequently complicated by hepatocellular carcinoma (HCC), and primary hepatic vein thrombosis is not. The major cause of thrombosis is a hypercoagulable state in hepatic vein thrombosis, but more of the latter cases are idiopathic. The clinical presentation of the latter is milder, and onset is frequently inapparent, whereas the former is more severe, sometimes causing acute hepatic failure. Markedly enlarged subcutaneous veins over the body trunk characterize the latter. We propose that these two disorders be clinically distinguished with a suggested term "obliterative hepato-cavopathy" for the latter against classical BCS.