Purpose: To evaluate the visual outcomes after idiopathic epiretinal membrane surgery in glaucomatous and nonglaucomatous eyes and factors related to unfavorable outcomes in glaucomatous eyes.Methods: This was a retrospective cohort study including patients undergoing idiopathic epiretinal membrane surgery with $12-month follow-up. Final visual acuity at pseudophakic status was compared among groups of glaucoma, glaucoma suspect, and nonglaucoma and correlated with optical coherence tomography and visual field characteristics in patients with glaucoma.Results: Of the 314 patients enrolled, 31 had glaucoma and 22 were glaucoma suspect. Baseline visual acuity and central foveal thickness were similar across the groups. Most patients had improved/stable visual acuity postoperatively, with a lower proportion of 83.9% with glaucoma than 96.9% and 100% without glaucoma and glaucoma suspect, respectively (P = 0.002). The mean visual acuity did not change in the glaucoma group (from 6/29 to 6/23), but it improved from 6/25 to 6/12 (a gain of 16.7 approxETDRS letters) in nonglaucoma and 6/26 to 6/14 in glaucoma suspect (a gain of 14.0 approxETDRS letters) (both P , 0.001). The change of visual acuity was correlated with preoperative visual field defects (P , 0.001, r 2 = 0.554). Patients with glaucoma with more advanced, fixationthreatening defects or temporally located inner nuclear layer microcysts were more likely to have worsened visual acuity.Conclusion: Visual field testing is imperative for patients with glaucoma before idiopathic epiretinal membrane surgery for outcome assessment.