© 2017, Medical Association of Thailand. All rights reserved. Objective: To determine the preoperative variables affecting early and late favorable outcomes of bilateral lateral rectus recession surgery for concomitant exotropia. Material and Method: A retrospective study of 65 patients with concomitant exotropia (constant and intermittent) who had bilateral lateral rectus recession was conducted. The follow-up period was more than 1 year in all patients. Preoperative parameters were obtained and evaluated using univariate analysis. Results: Sixty-five patients with concomitant exotropia who underwent bilateral lateral rectus recession were included. In the early and late postoperative outcome, 78% and 82% of the patients were in the success group, respectively. Meanwhile, 22% and 18% were in the failure group, respectively. There was no association between postoperative outcome and preoperative variables i.e. age at onset (p = 0.841, 0.591), age at surgery (p = 0.564, 0.634), interval between onset and surgery (p = 0.506, 0.753), preoperative deviation (p = 0.278, 0.211), refractive error (p = 0.217, 0.136), anisometropia(p = 0.946, 0.946), phase of exotropia (p = 0.741, 0.013), A-V pattern (p = 1.000, 1.000), stereopsis (p = 0.841, 0.268) and amblyopia (p = 0.569, 0.567). Conclusion: Preoperative variables could not be used to predict the early and late postoperative outcome.