Purpose: To assess the impact of combined phacoemulsification-vitrectomy and sequential surgery for idiopathic epiretinal membrane (ERM) on refractive error (RE) and macular morphology. Methods: In this prospective clinical trial, we allocated phakic eyes with ERM to (1) cataract surgery and subsequent pars plana vitrectomy (PPV) (CAT group), (2) PPV and subsequent cataract surgery (VIT group) or (3) phaco-vitrectomy (COMBI group). Examinations were at baseline, one month after each surgery, and at 3 months and 12 months of follow-up. Primary outcome was the RE (the difference between predicted and achieved spherical equivalent); secondary outcomes were best-corrected visual acuity (BCVA), and incidence of cystoid macular oedema (CME) defined as >10% increment of central subfield macular thickness (CSMT). Results: Sixty-two eyes were enrolled. The mean RE showed a small myopic shift of -0.36D in all groups 1 month after surgery, decreasing after 12 months to -0.17D. The absolute value of the RE (ARE) ranged 0.49-0.68D after 12 months. In the immediate postoperative period, there was a higher incidence of CME in the CAT group. There was no significant difference in final RE, ARE, BCVA and CSMT between the groups. Four cases (17%) in the CAT group had resolved visual complaints and improved BCVA after cataract surgery resulting in no need for PPV within the follow-up period. Conclusion: Surgery for idiopathic ERM in phakic eyes with either phaco-vitrectomy or sequential surgery are equal approaches with respect to functional- (RE, BCVA) and anatomical outcomes (CME, CSMT). However, if starting with cataract surgery, 17% of the cases may not need subsequent PPV.