Thirty-five patients with central retinal vein occlusion had an extensive medical and laboratory evaluation to identify possible etiologic factors. We describe the natural course of the two forms of retinal venous occlusive disease, hemorrhagic retinopathy and venous stasis retinopathy, by observing a group of 25 untreated patients from one to eight years. Systemic vascular disease was most commonly associated with retinal venous occlusive disease. The visual prognosis is favorable in venous stasis retinopathy and extremely poor in hemorrhagic retinopathy. However, two of ten patients with venous stasis retinopathy developed hemorrhagic retinopathy with poor visual outcome.