The longer-term progression of retinopathy was observed in a previously described group of 85 diabetic patients enrolled in the Early Treatment Diabetic Retinopathy Study. The probability of progression to severe retinopathy was significantly greater for eyes with the following baseline characteristics: greater overall retinopathy severity, higher fluorescein leakage, higher capillary nonperfusion, and lower electroretinographic oscillatory potential amplitudes. The summed amplitudes of the oscillatory potentials, the overall severity of retinopathy, and the severity of fluorescein angiographic leakage were found to be independent predictors of progression to severe proliferative retinopathy in a regression model; capillary nonperfusion was not found to predict progression independently when fluorescein leakage was included in the model. Probability curves based on the regression model can be used to support clinical decisions concerning when to perform panretinal laser photocoagulation and how often to follow up patients with less than severe proliferative diabetic retinopathy.