STUDY DESIGN: Randomized controlled trial with pretraining, posttraining, and follow-up repeated measures. OBJECTIVE: To determine the effectiveness of a 4-week elastic resistance exercise program on balance in subjects with and without a history of sprained ankles. BACKGROUND: Several researchers have suggested that improving balance may help alleviate the symptoms of functional ankle instability and reduce the rate of recurrent ankle sprains. METHODS AND MEASURES: Forty subjects (20 males, 20 females; 20 subjects with chronic ankle instability [CAI], 20 healthy) participated in the study. Ten subjects (5 males, 5 females) from each CAI and healthy group were randomly assigned to either the exercise or control group, resulting in a total of 4 groups. Total travel distance of the center of pressure, monitored using a force platform, was measured before training, after 4 weeks of training, and at a 4-week follow-up. RESULTS: There were no interactions between gender, ankle sprain history, or training groups. Balance significantly improved in subjects with and without a history of ankle sprains following 4 weeks of elastic resistance exercises. Mean improvement in balance for the exercise group following training, reflected through a decrease in total travel distance, was -11.1 cm (95% confidence interval: -14.0 to -8.2 cm). These improvements in balance were retained 4 weeks after training. CONCLUSIONS: Balance was improved after 4 weeks of elastic resistance exercise in subjects with and without a history of lateral ankle sprains. Balance improvements persisted 4 weeks following the treatment cessation.