Visual acuity after cataract surgery in patients with glaucoma cannot be predicted accurately. We studied preoperative recordings of pattern visual evoked cortical potentials (PVECPs) to evaluate postoperative vision in patients with glaucoma and cataract. Fifty patients with glaucoma and no cataract and 31 patients with glaucoma and cataract who underwent phacoemulsification were included in this study. Age and P100 component significantly correlated with postoperative visual acuity with multiple linear regression analysis. A significantly greater number of patients with glaucoma, cataract, and a P100 component preoperatively showed a visual acuity of 0.7 or better postoperatively, as compared to those without a P100 component. PVECP before cataract surgery was able to predict postoperative good visual acuity in patients with glaucoma and cataract.