Recently, while investigating possible candidates for cardiac surgery, the author encountered 5 cases of an unusual pattern of systemic venous drainage. These patients appeared to have no inferior vena cava. Instead, blood from the lower extremities and kidneys drained into a large posterior azygos vein which eventually ascended into the thorax and emptied into the superior vena cava (Fig. 1). This anomaly has traditionally been called “absence of the inferior vena cava” and is also known as “persistence of the supracardinal vein.” It is more correctly termed “infrahepatic interruption of the vena cava with azygos continuation” (2). The malformation has been mentioned only rarely in the literature of American radiology (1, 6). Several references, however, appear in the pediatric literature, the most comprehensive being the recent review by Anderson et al. (2). This condition per se is harmless. Until the advent of cardiac catheterization and angiocardiography, the few reported examples were almost all discovered at autopsy. Now, cases associated with severe cardiac and extracardiac anomalies, often producing cyanosis, are being discovered antemortem. The pertinent features in our 5 cases are presented in tabular form rather than as individual case reports (Table I). Roentgenologic findings are discussed separately. Embryology In the embryo, the supracardinal vein runs in the dorsal aspect of the body. It empties cranially into the common cardinal vein, the anlage of the superior vena cava (Fig. 2). The three segments of the supracardinal vein have separate fates. The lowermost portion becomes the postrenal segment of the inferior vena cava. The uppermost portion becomes the azygos vein. The midsegment is obliterated. The upper end of the inferior vena cava is formed by other embryonic veins (the efferent veins of the liver). If these fail to develop properly, blood from the lower extremities and abdomen is forced to continue through the entire length of the supracardinal vein. Thus, the middle segment of the supracardinal vein does not regress, and the anomaly described herein results (5). Roentgen Findings If no associated anomalies are present, the findings on plain roentgenograms may well be normal. It is logical to expect azygos enlargement because of the large volume of blood carried by this vessel. This finding has been reported but rarely, however (2, 6). Most of the roentgenographic changes are related to the associated anomalies. All our cases showed cardiac enlargement and increase in the pulmonary vascularity, reflecting increased pulmonary blood flow, and all were admixture type lesions with either a single ventricle or a large ventricular septal defect. The angiographic findings are striking.