Mastocytosis is a heterogeneous group of disorders characterized by abnormal growth and accumulation of mast cells in one or more organs. Systemic variants of disease can be regarded as myeloproliferative disorders. Similar to other myeloid neoplasms, systemic mastocytosis shows a variable clinical course and prognosis and can progress into frank leukemia. The treatment of mastocytosis must be adjusted to the individual situation in each patient and the subtype of disease.