Five patients with carotid artery occlusive disease had unilateral visual loss in bright light. All five had reduced retinal artery pressure on the side of the visual loss, and arteriograms showed either an occlusion or a high-grade stenosis of the ipsilateral internal carotid artery. Unilateral visual loss in bright light may indicate ipsilateral carotid artery occlusive disease and may reflect the inability of borderline circulation to sustain the increased retinal metabolic activity associated with exposure to bright light.