A 12 year old male castrated Australian Shepherd presnted in June 2003 to Cornell University for progressive right hindlimb lameness of three months duration, unresponsive to medical management. Left stifle radiographs revealed an aggressive bone lesion in the proximal left tibia characterized by boney and cortical lysis, and a long zone of transition. Differential diagnoses for a primary bone tumor included osteosarcoma, chondrosarcoma, fibrosarcoma, and hemangiosarcoma. Osteosarcoma was considered most likely due to the patient's signalment, histopathology definitively diagnosed appendicular chondrosarcoma. Prognosis for chondrosarcoma in dogs is good if the tumor can be diagnosed early and resected completely and is believed to be better than for osteosarcoma. Compared to osteosarcoma, chondrosarcoma is less locally aggressive, grows more slowly, has a lower metastatic rate and is associated with a longer survival time. The prognosis is also influeced by the tumor location and by whether complete surgical excision is possible or not. This case report will discuss the diagnostics, prognostic indicators and treatment options for chndrosarcoma compared to osteosarcoma.