Mastocytosis (MC) encompasses a range of disorders characterized by a clonal, pathological accumulation of mast cells having a somatic activating mutation of the tyrosine kinase receptor Kit (exon 17, codon 816; D816V) in more than 90 % of adult patients. The mutation is much less common in children. Skin and bone marrow are most often affected. Symptoms and clinical course are very heterogeneous due to a variable degree of local or systemic mediator release or organ dysfunction as a result of mast cell infiltrates. Pruritus, wheals, flushing and gastrointestinal symptoms are often reported. The majority of pediatric patients experience spontaneous remission of MC. Adults usually have chronic disease, rarely transforming into an aggressive or lethal type. Indolent systemic MC with involvement of skin and bone is the most common type. In MC the risk for anaphylactic reactions following an insect sting (and other causes of mast cell activation) is increased significantly. Diagnostic hallmarks are biopsies from skin and bone marrow using tryptase antibodies for staining as well as serum tryptase levels. At present a curative treatment for MC is not available. Systemic histamine H(1) receptor antagonists are widely used. Aggressive types of MC respond partially to IFN-alpha or cladribine. A variety of receptor tyrosine kinase inhibitors is still under critical evaluation for systemic treatment of MC. After introduction of the WHO classification for MC and the development a German MC guideline, as well as the foundation of national and international competence networks for MC, a significantly improved quality of medical care for MC patients can be expected for the future.