Purpose: To analyze clinical, radiological and pathological features as well as clinical outcome after surgical treatment of patients with secondary chondrosarcoma arising from osteochondroma(tosis). Materials and Methods: We retrospectively reviewed clinical records, radiographs, pathologic slides of 14 patients. Nine patients were male and fi ve were female. The mean age was 34 years. The mean follow-up period was 54 months. Results: All patients had a history of previous mass since childhood or puberty. Preexisted osteochondroma was single in 3 patients and multiple in 10. Remaining 1 patient had multiple osteochondromatosis with enchondromatosis. MRI clearly provided thickness of cartilage cap, which was over 2 cm except in 2 cases. Chondrosarcoma was grade 1 in all except 1 case, which was grade 2. Wide excision was performed in 10 patients, marginal excision in 3 and amputation in 1. Twelve patients were doing very well without evidence of disease. Among 3 patients with marginal excision, 1 patient had local recurrence and 1 patient died of disease. Conclusion: Comprehensive understanding of clinical, radiological and pathological features of secondary chondro sarcoma is warranted for accurate diagnosis. The best result can be expected with early recognition of malignant change of osteohcondroma(tosis) and wide excision.