In 1869, Nettleship1described an unusual type of urticaria which bears the name urticaria pigmentosa. For the next 80 years it was regarded as a comparatively rare skin condition characterized by yellow or brown macules or nodules, which, when rubbed vigorously, produced a whealing or urtication localized to the pigmented areas. Apart from the occasional report of rare solitary nodular and bullous lesions, the only other significant observation during this period was the finding of Unna,2in 1887, that the skin manifestations of urticaria pigmentosa were characterized by a marked infiltrate of tissue mast cells. In 1949, Ellis3reported the first case of urticaria pigmentosa in which an autopsy was performed. This one-year-old Negro girl had the typical skin lesions of urticaria pigmentosa from birth, associated with gastrointestinal upsets and hepatosplenomegaly. The autopsy revealed increased numbers of mast cells in the areas of portal