Fibrous dysplasia (FD) is a non-neoplastic developmental hamartomatous disease of the bone, characterised by a blend of fibrous and osseous elements in the region. It is a lesion of unknown etiology, uncertain pathogenesis, and diverse histopathology. With an incidence of 1:4000-1:10,000 it seems to be a rare disease. It represents approximately 2.5% of all bone lesions and about 7% of all benign bone tumors. The objective of this paper is to present an unusual case of Fibrous Dysplasia. A patient with chief complaint of pain and swelling in right side of the mandible was examined. OPG showed poorly defined mixed density pattern. Ultrasound of thyroid revealed enlarged nodes. CBCT revealed hypodense area. CT also showed features of osteomyelitis. Bone scan suggested fibrous dysplasia, which was confirmed by biopsy. Patient also had deficiency of Vitamin D.