A hilar cholangiocarcinoma is a cholangiocarcinoma occurring at the confluence of the right and left hepatic bile ducts which is called as Klatskin tumor. Because hilar cholangiocarcinoma is the most common form of extrahepatic bile duct cancer (EBDC), the epidemiology and risk factors of hilar cholangiocarcinoma are similar to those of EBDC. In Korea, overall incidence of EBDC is 5.1/100,000 individuals without a significant change during past 10 years. Most of cases occur in patients over the age of 50 and the incidence is 1.78 times higher in men than women. The etiology of EBDC has not been clearly defined. A number of pathologic conditions, however, resulting in either acute or chronic biliary tract epithelial injury may predispose to malignant change. Chronic biliary tract parasitic infection, such as Clonorchis sinensis and Opisthorchis viverrini, has been identified as a risk factor of EBDC and hilar cholangiocarcinoma. Other clear risk factors of EBDC are primary sclerosing cholangitis and choledochal cyst. However, there are no enough evidences whether primary sclerosing cholangitis and choledochal cyst are the definite risk factors of hilar cholangiocarcinoma or not. (Korean J Med 79:593-596, 2010)