Mastocytosis refers to a spectrum of clinical and laboratory abnormalities attributable to tissue infiltration by large numbers of mast cells and to the discharge of various biologically active substances by these cells. It most commonly results in cutaneous manifestations during childhood but may develop at any age or involve almost any organ system. The treatment of mastocytosis has become considerably more practicable in recent years with the availability of agents that directly inhibit mast cells or temporarily reduce their quantity in the skin.