A number of clinical conditions, most commonly seen in infants and children, caused by disease of Langerhans’ cell histiocytes. These cells, which are characteristic of all of the variants of the disease, cause granulomas. The great variation in the signs and symptoms produced depends upon their location and how widely spread they are. Almost any organ system including the skeleton may be involved. These diseases were previously given names such as histiocytosis X, Hand-Schiiller-Christian disease, Letterer-Siwe disease, and eosinophilic granuloma. Treatment may consist of surgical removal of bone lesions and radiation therapy for lesions threatening vital functions such as sight and hearing. Corticosteroids or cytotoxic agents are useful in controlling soft-tissue disease and multiple skeletal lesions. Bone marrow transplantation has been used in recurrent and progressive Langerhans’ cell histiocytosis.