Abstract
Mastocytosis is a clonal, neoplastic mast cell proliferation, which is in most cases restricted to the skin (cutaneous mastocytosis), but may infiltrate other organs as well (systemic mastocytosis). Involvement of the liver by a systemic mastocytosis with impairment of liver function has been recognized as sign of an aggressive course of disease (C-finding). This article presents a case of aggressive systemic mastocytosis in a 26-year-old male patient with involvement of the liver mimicking primary sclerosing cholangitis. By histology we could demonstrate multifocal clusters of atypical mast cells infiltrating portal tracts in intimate contact with bile ducts as the cause of cholangitis and liver fibrosis.