Forty-five patients with a central retinal vein occlusion were divided into three groups: those with venous stasis retinopathy (VSR, n = 27), those with hemorrhagic retinopathy (HR, n = 6), and those with undetermined retinopathy (n = 12). The electroretinogram (ERG) was recorded in all cases. The average b/a-wave amplitude ratio of the single white-flash ERG was 1.67 for the VSR group and 0.70 for the HR group. The ERG responses in the group with undetermined retinopathy helped to assess the degree of retinal ischemia and to further categorize the disorder as either VSR or HR. The b/a amplitude ratio reflected the degree of retinal ischemia and had prognostic value in predicting in which cases neovascular glaucoma may develop. The average b/a ratio in the six cases in which neovascular glaucoma developed was 0.84. This complication did not develop in any patient with a b/a ratio greater than 1. Four patients with low b/a ratios (average, 0.73) were treated with panretinal photocoagulation; neovascular glaucoma developed in none.