Erdheim Chester disease (ECD) is very rare non-Langerhans cell histiocytosis (LCH) which occurs in the skeletal system and multiple organs. As it is progressive, sometimes it causes fatal results. However, it is often misdiagnosed as LCH or multiple bone metastasis and, thus, is very difficult to diagnose. In Korea, only 10 cases were first reported in 1999. In particular, there have been a few orthopedic approaches or reports in English-speaking literatures, and no report has been issued in Korea. The authors performed bone biopsy in patients with knee and lower extremity pain who were referred for the integrated treatment. We attempts to report this diagnosis experience with literature review.