This prospective study aimed to quantify the retinal thickening induced by epiretinal membrane (ERM) peeling and to correlate this thickening with postoperative retinal function. Twenty-five patients who required surgery for idiopathic ERM were included in the study. The authors performed a macular OCT scan and microperimetry immediately before and three months after surgery. During membrane peeling, real-time OCT scans of the area being peeled were recorded. The increase in retinal thickness due to traction from the forceps was calculated as a percentage of preoperative retinal thickness. Areas of the retina that showed thickening during surgery were examined with microperimetry three months later. Transient retinal thickening occurred in 64% of patients, with a median thickening of 143%. Six patients were found to have new microscotomata after surgery, although half of these occurred without apparent retinal thickening. While this study shows that transient retinal thickening is common during ERM peeling, this does not appear to be related to the incidence of microscotomata.