Langerhans Cell Histiocytosis(Idiopathic Histiocytosis, Histiocytosis-X) is most often found in children and young adults, and cell proliferation with specific phenotype shows ultrastructural and immunohistochemical similarities with Langerhans Cells that normally exist in epithelium and mucosa. This disease occurs as single or multiple lesions in skull, ribs, vertebrae, mandible and long bones, and when it involves mandible, clinical sign and symptoms such as bone swelling and pain are noticed. When it involves alveolar bone, severe tooth mobility as well as gigival inflammation, proliferation, and ulceration are commonly found, and so it is not easy to differentiate it from general inflammatory diseases. Any local lesion at the tooth apex on the x-ray view needs to be differentiated from inflammatory disease, and multiple lesions from multiple ostoeoma and chronic multifocal osteomyelitis. This case is LCH in 51-pear-old male patient; this is a rare case, for the patient belongs to an age group with very low incidence rate of the disease. although three-timed biopsy tests and longterm observation at two university hospitals, it was misdiagnosed as multifocal osteomyelitis.