Implant- or fracture-associated neoplasia has been reported in humans and dogs, but the mechanism is unknown. Possible theories include metal implants acting as a nidus for continuing inflammation or corrosion of metal causing altered host reaction. In this study, the medical records of dogs undergoing tibial plateau levelling osteotomy (TPLO) at 2 different institutions (Clinics A and B) were reviewed to determine the incidence of osteosarcoma at the TPLO site and other sites. Records of 472 Clinic A dogs and 1992 Clinic B dogs with >1 year of follow-up were available for analysis. Both institutions used multiple plate manufacturers, although the majority of the plates were from 2 manufacturers. Of the dogs from Clinic A and Clinic B, 5 and 6 dogs developed osteosarcomas at the surgery site, and 7 and 22 dogs developed osteosarcoma at other sites, respectively. The incidence rate at the TPLO site was 30.4 and 10.2 per 10000 dog-years at risk and at other sites was 42.6 and 37.5 per 10000 dog-years at risk, respectively. For Clinic A, the median time for development of osteosarcoma at the TPLO site was 4.6 years; at other sites, it was 2.9. At Clinic B, median time was 4.4 years and 3.4 years. The authors concluded the risk for osteosarcoma development following TPLO surgery is low.