Retinal arterial macroaneurysms: risk factors and natural history. A case control study was conducted to identify the systemic and ocular risk factors for retinal arterial macroaneurysms. Forty-three patients with 52 photographically confirmed macroaneurysms were located. Forty-three age-matched, race-matched concurrent control patients were also identified. The patients with macroaneurysms had decreased visual acuity (p less than 0.0001) and a higher prevalence of hypertension (p = 0.037), female sex (p = 0.099), and retinal vein occlusions (p = 0.055) than controls. In patients with both a macroaneurysm and venous occlusion there was a 12.0 times higher prevalence of macroaneurysms in the area of retina drained by the occluded vein (p less than 0.05). Common findings associated with macroaneurysms included retinal haemorrhage (81% of patients), retinal exudate (70%), vitreous haemorrhage (30%), macular involvement (30%), and distal arteriolar narrowing (26%). Arteriolar occlusion occurred spontaneously (8%) or after laser photocoagulation (16%). 