Purpose: The purpose of this study is to analyze the clinical prognostic factors which may affect the postoperative clinical results of the unstable ankle fractures. Materials and Methods: This study is based on 62 unstable ankle fractures treated by open reduction and internal fixation from May 1994 to June 2000, with a minimum follow-up period of 12 months(range: 13 months-7 years 3 months). The 62 patients were average 39.1 years old with male: female ratio of 41:21. Based on Lauge-Hansen classification, the supination-external rotation type was the most common with 36 (58.1%) cases. The clinical results was assessed by American Orthopaedic Foot and Ankle Society(AOFAS) functional scale. The sex, age, body weight, trauma-operation interval, operation time, cause of injury, fracture type were statistically analyzed as the possible postoperative clinical prognostic factors. Results: Postoperative AOFAS functional scale was average 82.1 points with 22(35.5 %) cases excellent, 12(19.4%) good. 16(25.8%) fair and 12(19.4%) cases poor results. The age and the operation time were found to be statistically significant factors affecting the prognosis(p<0.001). The sex, weight, trauma-operation interval factors did not significantly affect the clinical results. The pronation-external rotation type showed better clinical tendency among the fracture types, but without the statistical significance. Conclusion: The surgically treated unstable ankle fractures in patients whose age was above 41 years old or operation time exceeding 90 minutes showed significantly poor clinical results.