A case suspected of eosinophilic granuloma of the left proximal tibial end was repoted. Eosinophilic granuloma is the most benign variant of histiocytosis X and may have spontaneous regression during course. When it occurs in infancy, it is important to differentiate from Letterer-Siwe syndrome, congenital generalized fibromatosis and metastatic neuroblastoma. Our case was a one-month-old girl whose left lower limb was noticed to be less active than the right one at ten days after birth. The roentgenographic appearance of the left proximal tibial end showed cystic osteolysis of spongiosa, periosteal new bone formation and partial cortical defect. About two months later, these findings disappeared without therapy and then there are no sing of reccurence or new focus.
