Systemic mastocytosis is a rare, often undiagnosed disease characterized by the proliferation of mast cells in several tissues. The clinical symptoms are related to the mast cell infiltrates, but also to the release of numerous mediators. Malignant mastocytosis is a term that refers to two different entities: aggressive mastocytosis, where the outcome with a myeloproliferative disease, where the latter governs the prognosis. The potential severity of these diseases justifies the development of more intensive therapeutic measures.