Osteosarcoma is a bone tumor and can occur in any bone, usually in the extremities of long bones, near the metaphyseal growth plates. Osteosarcoma of the jaw bones represents a distinct group of lesions from the conventional type commonly occurring in long bones. The emphasis should be laid on the aggressiveness of this lesion which warrants an early identification and diagnosis of the lesion followed by prompt treatment. True synchronous multicentric osteosarcomas of the jaws are extremely rare but, like other osteosarcomas of the jaws, have a favourable outcome, and palliative resection of such lesions, though challenging, can therefore lead to an enormously improved quality of life and self-image, and may even offer the opportunity for cure. We present a case of osteosarcoma of mandible in a young male treated by radical excision and reconstruction using free fibula bone flap.