Purpose To compare the outcomes of unilateral lateral rectus muscle re-recession and medial rectus muscle resection for treatment of recurrent or persistent exotropia. Design Retrospective nonrandomized clinical trial. Methods setting: Hospital-based clinical practice. patient population: Forty patients with recurrent or persistent exotropia following bilateral lateral rectus muscle recessions. intervention: Fourteen patients were treated with unilateral medial rectus muscle resection and 26 with unilateral lateral rectus muscle re-recession. main outcome measures: Outcomes were considered successful if the patients had deviations less than 10 prism diopters (PD) at last follow-up. All patients were followed for at least 1 year postoperatively. Results The mean preoperative deviations were 17.4 PD in the medial rectus muscle resection group and 18.1 PD in the lateral rectus muscle re-recession group. Successful outcomes were achieved in 9 of 14 patients (64%) treated with medial rectus muscle resection and 19 of 26 patients (73%) treated with lateral rectus muscle re-recession. There was no statistically significant difference between these outcomes. Mean follow-up was 4.5 years in the medial rectus muscle resection group and 2.9 years in the lateral rectus muscle re-recession group. Conclusions Surgery on a single muscle can be used to treat moderate-angle recurrent or persistent exotropia. Unilateral re-recession of the lateral rectus muscle and medial rectus muscle resection have equivalent success rates.