BACKGROUND We have developed a technique for the treatment of cataract and epiretinal membrane using a 25-gauge vitrectomy system through corneal ports. METHODS Randomized, prospective study, Toyama Prefectural Central Hospital, Toyama, Japan. METHODS Twenty eyes of equal patients scheduled for cataract surgery combined with vitrectomy. METHODS Twenty eyes with cataract and epiretinal membrane were received treatment with our newly developed system (clear corneal vitrectomy) or the standard 25-gauge pars plana vitrectomy with corneal incision cataract surgery. The newly developed system uses 0.5-mm wide corneal side ports located at the superonasal, superotemporal and inferotemporal positions. After phacoemulsification using corneal incision, an infusion cannula was inserted from the inferotemporal port. Then core 25-gauge vitrectomy was performed using the corneal three port. After the epiretinal membrane was removed using forceps, an intraocular lens was implanted into the capsular bag. Finally, all corneal incision wounds were hydrated. METHODS Visual acuity, intraocular pressure, corneal thickness, corneal endothelial cell and ocular inflammation were examined. RESULTS All procedures were uncomplicated in both groups. There was no leakage of aqueous humour from the corneal wounds in the developed system. There were no significant differences in visual acuity, corneal thickness and endothelial cell density loss. CONCLUSIONS Clear corneal vitrectomy would be a good option for selected cases with cataract and vitreoretinal diseases.