Systemic mastocytosis is characterized by mast cell proliferation in different organs. Classification delineates 4 categories: indolent systemic mastocytosis, systemic mastocytosis with an associated clonal hematologic non-mast cell lineage disease, aggressive systemic mastocytosis and mast cell leukaemia. Clinical manifestations are due to organ infiltration (skin, bone, gut, liver, spleen, lymph nodes) and release of mast-cell mediators. Diagnosis of mastocytosis is based on appropriate stains (Giemsa, Toluidine) and immunophenotype features (tryptase, CD117). Serum level of tryptase reflects the total burden of mast cells. Treatment must prevent mast cell mediators release (histamine antagonists, cromolyn sodium, corticosteroids, leukotriene-receptor inhibitors) and have a cytoreductive effect (interferon, cladribine, tyrosine kinase inhibitors).