Synchronous multifocal/multicentric osteosarcoma (SMOS) is a rare variant of osteosarcoma with fewer than 100 well-documented cases in the medical literature. SMOS affecting the jaw is even rarer with only three cases involving the mandible reefing been reported. We report here a case of a 16-year-old mentally challenged girl with SMOS. Radiological examinations showed sclerotic lesions in the left distal femur and in right mandible without pulmonary metastasis. Histological examination showed osteoblastic- ype osteosarcoma with chondroid differentiation. Despite high-dose chemotherapy the patient died after 6 months after the initial diagnosis. Immunohistochemistry revealed that p53 protein was positive in most of the tumor cells. The clinical course, radiological and histological appearance of the lesion indicated it was an SMOS rather than metastasis arising from a single osteosarcoma. This case could be regarded as powerful evidence to support the multicentric theory related to SMOS. 

Keywords: Synchronous; Multifocal; Multicentric osteosarcoma.