Forty patients with fatty liver were studied by peritoneoscopic examination after intravenous administration of indocyanine green (ICG). Although diffuse or centrilobular steatosis was observed in both nonalcoholic and alcoholic fatty liver, periportal steatosis was seen only in alcoholic fatty liver. Vascular markings were more prominent in alcoholic fatty liver, especially in those with fibrosis, compared with nonalcoholic fatty liver. Fat was not stained with ICG. Unstained red patches, observed after ICG administration in both nonalcoholic and alcoholic fatty liver, were thought to be due to congestion in the former and to lobular inflammation as well as congestion in the latter. Acinar markings were indistinct in the fatty liver with fibrosis but became clearer after ICG administration.