Hilar cholangiocarcinoma, first described by Klatskin in 1965, is a relatively rare tumor arising from the bile ducts. The histomorphological features of hilar cholangiocarcinoma are identical with other extra- and intra-hepatic bile duct carcinomas. The most common disease associated with cholangiocarcinoma is primary sclerosing cholangitis. The development of cholangiocarcinoma is a multistep process associated with several mutations in oncogenes and tumor-suppressor genes. Based on macroscopic appearance, three distinct subtypes have been described: sclerosing, nodular, and papillary. Microscopically, more than 95% of tumors are adenocarcinomas. Hilar cholangiocarcinoma is a slowly growing tumor and tends to spread longitudinally along the bile ducts with neural, perineural, and subepithelial extension. Lymph node invasion can be found in 30%-50% patients at the time of diagnosis, but blood-born metastases are rare and usually occur at late stages. © 2010 Higher Education Press and Springer-Verlag Berlin Heidelberg.