There are few reports on the surgical treatment of secondary malignancy arising from an osteochondroma on the lateral side of the proximal tibia. From March 2008 to December 2011, 3 patients were treated for a secondary chondrosarcoma from an osteochondroma of the proximal tibia involving the fibula. The operative procedure can be summed up as follows: (1) resection of the tumor including the fibula; (2) preservation of the peroneal nerve and the fibular head; and (3) arthrodesis of the proximal tibiofibular joint. Serial radiological studies showed successful fusion in the proximal tibiofibular joint in all patients. The Musculoskeletal Tumor Society functional scores were excellent in all 3 patients. No patients showed instability of the ipsilateral knee joint in any direction. All 3 patients could return to sports activities. Until the last follow-up, there was no evidence of disease recurrence. We suggest that the operative procedure described in this article would provide satisfactory oncological and functional outcomes.