The cases of forty-six patients who had dedifferentiated chondrosarcoma were reviewed. Two groups were identified: one in which a low-grade malignant chondrosarcoma was the precursor lesion and one in which a moderate to high-grade malignant chondrosarcoma was the precursor lesion. The radiographic features of these lesions ranged from that of a cartilaginous lesion that appeared to be benign to that of a destructive osteolytic tumor in which the cartilaginous component was overshadowed by the dedifferentiated component. Only three of the forty-six patients survived for more than two years. Resection alone, even when it was wide or radical, was not successful in controlling this lethal sarcoma.