Purpose: To analyze the result of Modified Brostr$ddot{O}$m procedure for Chronic ankle lateral instability without associated injury. Materials and Methods: Forty-one patients(Forty-one feet) diagnosed and operated with chronic ankle lateral instability without associated injury were evaluated retrospectively from June 1995 to December 1999. Twenty-three patients were athletes. For the evaluation of clinical outcome, a subjective grading scale of modified Hamilton was used, and pain relief, relief of instability symptom and anterior drawer test were evaluated. Results: Among forty-one operations, there were six excellent, thirty-five good results as a whole. All cases showed over the grade good. The average time to ordinary life in the non-atheletes was 2.5 months and average time to sport activity in the athletes was 4 months postoperatively. Conclusion: The modified Brostr$ddot{O}$m procedure seems to be effective method for chronic ankle lateral instability without associated injury.