Osteogenic sarcoma (OSA) is the most common malignant bone tumor in dogs. The etiology of canine OSA is largely unknown. Reports have noted an association between prior local radiation therapy, bone infarcts, and prior fractures (fixed with metallic implants) and the development of bony tumors. A hereditary basis for canine OSA has long been suspected by veterinarians, given the disproportionate incidence in many breeds. The Scottish Deerhound is a giant breed of dog with a ten percent estimated incidence of osteosarcoma. By studying family groups of dogs within this breed, we hope to determine both the mechanism of inheritance as well as the region of DNA associated with their high risk of developing OSA. Determination of the genetic regions (or genes) responsible for the high incidence of OSA in breeds such as the Scottish Deerhound will allow further understanding of the mechanisms underlying neoplastic transformation, enable genetic testing for carriers across all breeds, as well as present new therapeutic targets.