PHOTOS 1-2: Osteosarcoma is the most prevalent primary bone neoplasm in dogs. These neoplasms are mostly malignant and may cause death due to local infiltration or metastasis. They especially metastasize to the lungs in dogs. Osteosarcoma affects the appendicular or axial skeleton and occurs mostly in large and giant breed dogs. Some dogs are genetically predisposed to developing osteosarcomas. Appendicular osteosarcomas occur mostly in the metaphyses of the distal radius; femur or proximal humerus. Osteosarcomas are diagnosed radiographically and exhibit a lytic proliferative pattern in the affected bone. Pre-amputative diagnosis can be made by histopathological evaluation of bone biopsies. Amputation is the treatment of choice along with chemotherapy. If the owners of the animal understand the high risk of the animal dying of metastatic lung disease and if the clinical radiographic findings are suggestive of osteosarcoma, the limb can be amputated without histological diagnosis. An alternative to amputation is resecting the bone and using an allograft from a cadaver to replace the neoplastic bone. These animals are also treated with chemotherapy. The main complication of this limb sparing method is the development of osteomyelitis in the allograft which then makes amputation necessary.