The computed tomographic (CT) appearance of a case of intraductal mucosal-spreading mucin-producing peripheral cholangiocarcinoma of the liver is described in a patient presenting with acute pericardial tamponade due to rupture of the cystically dilated left intrahepatic ducts by mucin hypersecretion. CT showed cystic and tubular dilatation of the intrahepatic ducts of the left and caudate lobes, but there was no grossly visible tumor mass. Pathology showed a single layer of tall columnar tumor cells with short intraluminal papillary projections lining each bile duct; the ducts were markedly dilated because of excessive mucin secretion. There was no gross tumor mass in the bile ducts. The tumor spread diffusely and contiguously along the intrahepatic bile ducts, with minimal invasion to the bile duct wall. To our knowledge, there has been no report about mucosal-spreading peripheral cholangiocarcinoma of the liver.