We report here on a case of extrahepatic biliary cystadenoma arising from the common hepatic duct. A 42-year-old woman was evaluated by us to find the cause of her jaundice. Ultrasonography and CT showed a cystic dilatation of the common hepatic duct and also marked dilatation of the intrahepatic duct. Direct cholangiography demonstrated a large filling defect between the left hepatic duct and the common hepatic duct; dilatation of the intrahepatic duct was also demonstrated. Following excision of the cystic mass, it was pathologically confirmed as a unilocular biliary mucinous cystadenoma arising from the common hepatic duct.