The pathogenesis of proliferative diabetic retinopathy is unknown. Although there are some established clinical and histological facts, the exact sequence of events is yet to be determined. Diabetic angiopathy is widespread in the body and appears to be a complication ofand related to the duration of the diabetic state. The essential difference between this and proliferative diabetic retinopathy is the absence of microaneurysm formation and neovascularization outside the eye. It thus seems that local ocular factors, either genetic, metabolic, or anatomical, modify the generalized response. The role of the last factor has not yet been investigated, so that it is not known whether the anatomical pattern of the retinal arteries and veins has any relationship to the sites and size of areas of neovascularization. It is the purpose of this paper to study the size and distribution of those areas in early proliferative diabetic retinopathy which are of sufficient size to be visible in fundus photographs and to subject them to statistical analysis to see if any definable pattern emerges.