Primary sclerosing cholangitis is an increasingly recognized cause of chronic cholestatic liver disease. The etiology is unknown, although a number of immunologic and nonimmunologic factors have been considered. The most important diagnostic findings are diffuse irregularity and narrowing of extrahepatic and intrahepatic bile ducts. The prognosis varies, and a number of relatively unique complications may develop. No adequate treatment exists, although a number of potential treatments have been evaluated. Liver transplantation still remains the most appropriate treatment for end-stage disease. These various topics related to primary sclerosing cholangitis are reviewed.