The term mastocytosis is referred to as an array of uncommon, usually sporadic, heterogeneous clinical illnesses that result from the hyperplasia of tissue mast cells. It comprises many different clinical manifestations varying from indolent cutaneous forms to systemic and malignant conditions. The characteristic presentation of mastocytosis consists of cutaneous manifestations: either a solitary mastocytoma, urticaria pigmentosa, or less commonly, diffuse cutaneous mastocytosis. Urticaria pigmentosa is the most common manifestation of cutaneous mastocytosis that manifests as a generalized eruption of round or oval erythematous macules, papules and plaques with variable amounts of brown pigment, usually on the trunk, but may also occur in all regions of the body including face and mucous membranes. Pruritus, dermographism and Darier's sign are additional features of these eruptions. Mastocytosis may also be manifested as mastocytoma, a rare, benign, pediatric tumor that results from hyperplasia of mast cells in papillary dermis in the first few weeks of life. The clinical course of mastocytosis is variable. The prognosis for the majority of pediatric patients with urticaria pigmentosa is extremely good, and over half of cases clear completely by adolescence, while those with aggressive systemic mastocytosis or mast cell leukemia show a progressive course, usually with a fatal outcome.