PURPOSE: The purpose of this study is to analyze the clinical and radiographic prognostic factors which may affect the postoperative clinical results of the unstable ankle fractures. MATERIALS AND METHODS: This study is based on 75 unstable ankle fractures treated by open reduction and internal fixation from May 1994 to August 2000, with a minimum follow-up period of 12 months(range : 13 months-7 years 3 months). The 75 patients were average 40.5 years old with male: female ratio of 52:23. Based on Lauge-Hansen classification, the supination-external rotation type was the most common with 42 (56.0%) cases. The clinical results was assessed by American Orthopaedic Foot and Ankle Society(AOFAS) functional scale. The sex, age, side of injury, body weight, trauma-operation interval, operation time, cause of injury as the possible postoperative clinical prognostic factors and fracture type, anatomical reduction of fracture, preoperative medial clear space, postoperative medial clear space, talo-crural angle, talar tilt, tibio-fibular clear space, tibio-fibular overlap space as the possible radiographic prognostic factor were statistically analyzed RESULT: Postoperative AOFAS functional scale was average 81.0 points with 23(30.7%) cases excellent, 17(22.7%) good, 18(24.0%) fair and 17(22.7%) cases poor results. The age, the operation time(p<0.001) and the anatomical reduction of fracture(p<0.005) were found to be statistically significant factors affecting the prognosis. The other clinical and radiographic factors did not significantly affect the clinical results. CONCLUSION: The surgically treated unstable ankle fractures in patients whose age was above 41 years old or operation time exceeding 90 minutes or unsatisfied anatomical reduction of fractures showed significantly poor clinical results.