We present a woman with chondroblastic osteosarcoma of the left ilium extending to the L4 epidural space and invading the inferior vena cava and right atrium, misdiagnosed as deep venous thrombosis. After neoadjuvant chemotherapy, two stage resection was planned. During the anterior approach, a mass in the left common iliac vein and inferior vena cava was found and tumor thromboembolism was diagnosed. Frozen sections showed chondroblastic osteosarcoma. The patient denied further surgery and had palliative intensity modulated radiation therapy
