ABSTRACT— Cirrhosis of the liver was diagnosed in an 18-year-old man with histiocytosis X. Electron microscopy and immunohistochemistry revealed infiltration of the liver by the typical cellular elements of histiocytosis X. Endoscopic retrograde cholangiography showed alterations resembling those of sclerosing cholangitis. Sixteen months later, the patient died of recurrent variceal bleeding and cholangiosepsis. Autopsy confirmed that cirrhosis was the main manifestation of the underlying disease. Thus, cirrhosis of liver can be a main and potentially fatal manifestation of histiocytosis X beyond the pediatric age range. Histiocytosis X may lead to parenchymal infiltration of the liver and to changes of the major bile ducts resembling sclerosing cholangitis. The diagnosis of hepatic histiocytosis X can easily be missed without relying on appropriate electron microscopic and immunohistochemical investigations.