Purpose: To investigate anatomic changes in retinal thickness (RT) and functional changes after vitrectomy for idiopathic epiretinal membranes (ERMs) with and without internal limiting membrane (ILM) peeling. Methods: The medical records of 100 eyes of 96 patients with ERM who underwent vitrectomy and ERM removal were reviewed retrospectively. The RT was measured by optical coherence tomography, and the area was divided into 9 sections. The best-corrected visual acuity (BCVA), 9 RT areas, and incidence rates of recurrent ERM were compared between the groups with and without ILM peeling before the operation and 12 months postoperatively. Results: Thirty-nine eyes that underwent vitrectomy with ILM peeling and 61 eyes that underwent vitrectomy without ILM peeling met the inclusion criteria. There were no significant differences between the groups in the BCVA and any of the RTs before the operation and 12 months postoperatively. The ERMs recurred in 8 (20.5%) of 39 eyes and 26 (42.6%) of 61 eyes in the groups with and without ILM peeling, respectively, with a difference that reached significance (p = 0.02) 12 months postoperatively. Conclusions: Vitrectomy for ERM affects the BCVA or the RTs 12 months postoperatively. Additional ILM peeling does not affect them, but it might reduce the ERM recurrence rate.