OBJECTIVE. The pericardiacophrenic vein is a possible route of collateral circulation when either the superior or the inferior vena cava is obstructed. When the vein is dilated, it can cause an abnormal appearance on chest radiographs. We describe four such patients. MATERIALS AND METHODS. We studied four patients who had abnormalities on conventional chest radiographs due to a grossly dilated pericardiacophrenic vein, confirmed by means of venacavography, CT, or MR imaging. We analyzed the cause of the dilatation and the radiologic findings associated with the dilated pericardiacophrenic vein. RESULTS. The cause of the dilated pericardiacophrenic vein was the membranous obstruction of the inferior vena cava in all four patients. Chest radiographs revealed an undulating vascular shadow (in two cases) or a shadow of several masses (in one case) along the left border of the heart or a poorly defined haziness mimicking a pulmonary parenchymal infiltrate (in one case). A direct communication between the left hepatic vein and the left inferior phrenic vein was seen near their insertion into the inferior vena cava in three cases. Hepatic venous outflow and some of the systemic venous return were directed to this left inferior phrenic-pericardiacophrenic route. CONCLUSION. When obstruction of the inferior vena cava is clinically suspected and the chest radiograph shows abnormalities at the left paracardiac area, a dilated pericardiacophrenic vein due to obstruction in the suprahepatic portion of the inferior vena cava, most likely a membrane, should be considered in the differential diagnosis.