A 6-yr-old maned wolf (Chrysocyon brachyurus) was diagnosed with an extraosseous osteosarcoma on the lateral aspect of the right thigh. Antemortem radiography revealed a calcified mass with no skeletal involvement. The mass was excised, but visible regrowth of the tumor was evident within 5 wk. Histologic examination and immunohistochemistry, including staining for p53 tumor suppression gene protein, were performed on the excised mass. The maned wolf was euthanized 13 wk after the initial diagnosis. The neoplasm was located in a site commonly used for the delivery of intramuscular injections, including vaccinations. Although no definitive association can be made, it is worth noting this relationship, as vaccine-site neoplasias have been observed in other species, most notably the domestic cat (Felis domesticus).