The objective of our clinic-based case-control study was to identify risk factors for branch retinal vein occlusion. Between 1986 and 1990 data were obtained at five clinical centers from 270 patients with branch retinal vein occlusion and 1,142 controls. Data were collected from interviews, clinical examinations, and laboratory analyses of blood specimens. An increased risk of branch retinal vein occlusion was found in persons with a history of systemic hypertension, a history of cardiovascular disease, an increased body mass index at 20 years of age, a history of glaucoma, and higher serum levels of alpha 2-globulin. Risk of branch retinal vein occlusion decreased with higher levels of alcohol consumption and high-density lipoprotein cholesterol. The data suggest a cardiovascular risk profile for patients with branch retinal vein occlusion and indicate that 50% of patients with branch retinal vein occlusion may be attributable to hypertension. Our findings support current public health recommendations to diagnose and treat hypertension, reduce weight, increase physical activity, and maximize serum high-density lipoprotein levels.