Purpose: We analyzed the ankle bony abnormality of patients with marked ankle instability who had chronic ankle sprain more than 3 years. Materials and Methods: We evaluated the chronic ankle sprain (more than 3 years) patients with marked ankle instability tested by varus stress test and anterior draw test from March 2000 to December 2005. Eighty-nine patients (104 ankle) were evaluated and there were 38 males and 51 females. The mean age of patient at the time of diagnosis was 34.5 (range, 18 to 56 years). The average duration of morbidity was 7 years and 3 months (range, 3 years and 3 months to 21 years). The patients who had history of dislocation, fracture, malalignment, operated patients, and rheumatoid ones were excluded. Plain radiographs of AP, lateral, oblique and mortise view were checked. Results: Radilologic abnormalities were found at 74 ankles (71%) among 104 ankles. Frequent sequences of location were anterior talotibial osteophyte, medial malleolar osteophyte, Os subfibulare, lateral malleolar osteophyte. Posteior osteophyte, ankle arthritis, talar articular defect were rarely found. Conclusion: Seventy-one percent among patients with chronic ankle sprain and marked ankle instability showed more than one radiologic abnormalities. Thus, more exclusive and accurate ankle examination should be performed in these patients.