SummaryA child, three months old, showing bones defects of the skull associated with cutaneous lesions of a papulous type is studied. A biopsy of the skull tumors showed an eosinophilic granuloma.Later on the clinical picture was that of Letterer-Siwe’s disease : fever with hepatic and splenic enlargement, severe hypochromic anemia and extensive infiltration of the lungs with dyspnoea and cyanosis. The child died three months after the first symptoms appeared. Pathological study showed a reticular proliferation in the nodes, thymus, lunga, liver, spleen, lymphoid nodes of the bowel and skin.In the lymph nodes the picture was somewhat comparable to that of Besnier-Boeck’s disease. In the thymus the cells were frequently filled with lipoids, partly birefringent.This cass brings some support to the view that eosinophilic granuloma of the bones, Schüller-Christian’s and Letterer-Siwe’s diseases have a common basis. All three are characterised by a reticular proliferation. It seems that Schüller-Christian’s disease must be separated from the other diseases grouped as lipoidosis.The evolution of the disease here studied as well as the histological picture suggest an infectious origin, but no confirmation has been brought until now.The prognosis of eosinophilic granuloma is generally benign although in some rare cases general involvement leading to the Letterer-Siwe’s syndrom occurs. No therapy has been proposed in the generalized form.