In 1898 Marcus Gunn described the changes in retinal vessels noted with hypertension. Arteriolar narrowing, caliber irregularity, alterations of the light reflex, and hiding of the arterial blood column were noted. Arteriovenous crossing changes and capillary bed abnormalities, such as cotton-wool spots, retinal hemorrhages, and retinal edema were also mentioned, as well as blurred discs. In the 83 intervening years, little has been added to the description of hypertensive retinopathy, but our understanding has increased. Retinal vessels respond to elevations of systemic blood pressure by generalized arteriolar constriction. This can lead to arteriolar necrosis, retinal edema, cotton-wool spots, hemorrhage, and disc edema. If the blood pressure is controlled, or slow rising, or if arteriolar sclerosis is present in the retinal arteries, then a picture of arteriolar irregularity will be noted and, depending upon the ability of the retinal vessels to contract, segmental constriction will be seen. In separating hypertensives from nonhypertensives, the most consistent ophthalmoscopic finding is arteriolar narrowing with focal irregularity. In prognosticating for survival, the best method available is the Keith-Wagener-Barker classification. However, the difficulty in separating Groups 1 and 2 of this classification has lead to numerous modifications that make comparisons from one study to another difficult.