Hepatic artery collaterals in 40 patients who had had hepatic artery occlusion following peripheral or central embolization, surgical ligation, intra-arterial chemotherapy, or intimal injury from catheterization were studied. The collaterals were classified as intrahepatic or extrahepatic collaterals. Intrahepatic arterial collaterals develop in the portal triads and subcapsular area between the lobes of the liver. Extrahepatic arterial collaterals develop in the ligaments that suspend the liver in the peritoneal cavity and through the structures that are closely attached to the liver. A simplified angiographic classification of hepatic arterial collaterals is presented.