Osteosarcoma (OS), which is sometimes referred to as osteogenic sarcoma, is the most common primary bone tumour in adolescents and young adults. Mandibular and maxillary osteosarcomas account for 6% to 9% of all the osteosarcomas. Mandibular OS is often considered as a distinct entity because of its predilection to older patients (mean age: 34 to 36 years). The WHO has recognized several variants of OS that differ in location, clinical behaviour, and the degree of cytologic atypia. The most frequently occurring variant is the classical osteosarcoma which arises centrally within the bone . IT is a tumour that can occur in any bone but which most commonly occurs in the long bones of the extremities, near the metaphyseal growth plates. Osteosarcomas accounts for about 20% of all the sarcomas and about 4%-6% occur in the maxillofacial region. Sometimes, they are referred to as gnathic osteosarcomas The purpose behind writing of this case report was to highlight the diagnostic difficulties encountered in a patient of OS which affected the mandible and presented as a swelling in the lower right third molar region.