AIM: To evaluate the effect of prophylactic administration of nepafenac in prevention of macular edema occurring in diabetic patients after phacoemulsification and to investigate the correlation between optical coherence tomography (OCT) foveal thickness and multifocal electroretinogram (MF-ERG) parameters. METHODS: The study included two groups. Group 1 included 50 diabetic patients with senile cataract (50 eyes, 30 females, 20 males, aged 55±7y) received nepafenac 0.1% eye drop. Group 2 included another 50 diabetic patients with senile cataract (50 eyes, 22 female, 28 males, aged 53.8±8y) did not receive nepafenac. All patients were followed up for 3mo postoperatively. OCT and MF-ERG were done preoperative and at 1wk, 1, 2 and 3mo. RESULTS: The mean foveal thickness was statistically significantly lower in Group 1. Five eyes in Group 2 developed clinical cystoid macular oedema (CMO) (10%), and no patients in Group 1 developed central macular thickening more than 50 μm. There were insignificant differences in MF-ERG amplitudes and latencies between the two groups except in the five eyes that developed CMO, there statistically significant reduction of MF-ERG amplitude with increase in foveal thickness. CONCLUSION: Perioperative nepafenac reduces the incidence of CMO following uncomplicated phacoemulsification significantly. Nepafenac has no side effects.