Erdheim Chester is a rare histiocytic infiltrative disease characterized with bilateral symmetrical sclerotic involvement of the metaphyses and diaphyses of long bones. Fifty-one years old male patient presented with dull knee and leg pain which was present for two years and did not respond to non-steroidal anti-inflammatory medication was evaluated. His physical examination was normal. His X-rays revealed areas of symmetrical heterogeneous sclerosis in bilateral proximal tibial and distal femoral metaphysodiaphyseal regions. Laboratory findings revealed a mild increase in blood phosphorus levels and a significant increase in urine calcium level. Bone scintigraphy revealed an increased uptake in bilateral proximal tibias, distal femurs and distal end of the left tibia. Abdominal, chest and cranial radiological evaluations were all normal. There were no abnormal findings in bone marrow biopsy. His open bone biopsy obtained from the left proximal tibia revealed foamy lipid-loaded histiocytes, incipient local inflammatory reaction, rare giant cells and osteosclerosis with medullar fibrosis. The patient was given bisphosphonate treatment (Alendronate 70mg/week). There was a decrease in his leg pain in postoperative 1 year follow-up. Although Erdheim-Chester's is a rare disease, orthopedic surgeons should keep this disease in mind, in the differential diagnosis of patients who present with bone pain and sclerosis.