Purpose To determine whether the inferior oblique (IO) muscle weakening procedure combined with exotropia surgery affects the surgical correction of exotropia. Design Institutional, retrospective study. Methods We retrospectively reviewed the medical records of 310 patients who had undergone exotropia-correcting surgery combined with IO weakening (group A, 64 patients) or without IO weakening (group B, 246) with a postoperative follow-up of 6 months or more. The main outcome measures were the postoperative mean angle of horizontal deviation, the success rate, and the overcorrection rate. Surgical success was defined as an alignment between 10 prism diopters (PD) of exodeviation and 5 PD of esodeviation. Results The postoperative mean angles of exodeviation, throughout the follow-up period, did not significantly differ between the groups. Although the surgical success rate was higher in group B at postoperative 1 month (p = 0.035), there was no statistical difference between the 2 groups from postoperative 6 months.: The final success rates were 56.3 and 51.6% (p = 0.509). The overcorrection rate was significantly higher in group A at postoperative 1, 6 and 24 months (p = 0.017, p = 0.028, p = 0.030, respectively); however, at the final follow-up, there was no overcorrection in either group. Conclusion The overcorrection rate was higher in group A until postoperative 2 years, even though the mean angles of exodeviation and the success rates did not significantly differ between the 2 groups. Surgeons should be mindful of overcorrection when planning exotropia surgery combined with the IO weakening procedure.