SINCE there are so few reports of intraocular involvement by histiocytosis X, we think this case, in which the disease severely affected the iris and ciliary body, deserves reporting. Histiocytosis × is the name given by Lichtenstein1to the group of nonlipid reticuloendothelioses (eosinophilic granuloma), "Letterer-Siwe" disease, and "Schuller-Christian" disease. Report of a Case A 3-month-old female infant was first admitted to the hospital because of ulcerations in the mouth which were so painful that she would not feed at the breast. These ulcerations had been present for one week before admission. For two months prior to admission, she had been treated unsuccessfully for a severe generalized seborrheic dermatitis, most marked on the scalp. Physical Examination. —Her skin was covered with red, greasy, crusted maculopapular lesions. Petechiae were present, most obvious on the anterior chest wall, and there were purpuric lesions on the palms and soles. The ulcers of