Fibrous Dysplasia (FD) is a developmental disorder of bone that can affect one bone (monostotic type) or multiple bones (polyostotic type). The disease can be associated with hyperpigmentation and endocrinological disorders. In general, FD is found in teenagers, in the second decade of life. It often involves the long bones, craniofacial bones, ribs and pelvis. Approximately 30% of monostotic FD (MFD) lesions are found in the cranial, rather facial bones. It frequently appears in the posterior region of the jaw bone and is usually unilateral. The etiology of FD is not clear but even so genetic predisposition is suspected. The diagnosis is based on radiological and histopathological examination. We present an unusual case of symptomatic FD. A 15-year-old female patient was admitted to the clinic, complaining gradually increased swelling on her left side of the mandible one year ego with severe and unusual pain at related region. The bony enlargement was extending from median mandible to the crestal marginal level. Surgical shaving and recountering of mandible through the delicate preservation of the mental nerve in the left side of mandible was carried out. The aim of this report is to present the conservative treatment as sufficient treatment modality for the treatment of FD during puberty.