A case of Letterer-Siwe disease which confirmed by pathological and radiological examination, was reported. The patient was 13 months old male who had petechiae on the neck and abdomen, pallor and abdominal distension for6 months. His family history was not contributary. The roentgenograms revealed on oval shaped bony defect, about 2.5×1.5cm in diameter with sharp margin on the left parietal bone of the skull, and irregular bony destructivechanges in the vertebral bodies, pelvic bones, proximal one-fourth of the femora and the scapula. Biopsy specimen showed that the most lymphatic structures were replaced by proliferation of the relatively large histiocytes whichhad an oval nucleus with faint cytoplasm, and multinucleated histiocytes and giant histiocytes were also noted, but any necrotic areas were not visible.