In summary, chondrosarcoma arising in an osteochondroma is a difficult diagnosis to establish on radiological-morphological grounds, especially in low grade lesions. A patient with a painful, enlarging exostosis usually comes to require resection even in the absence of radiographic hallmarks of malignancy. Although many osteochondromas complicated by bursal formation will be resected for relief of symptoms, the identification of a reactive bursa surrounding an exostosis without grossly malignant features presages a benign course and will dramatically effect established preoperative plans.