Obsjective: To examine the relation between diameters of the retinal arterioles and 10 year incidence of hypertension. Design: Population based prospective cohort study. Setting: Beaver Dam eye study. Participants: 2451 normotensive people aged 43 to 84 years. Main outcome measures: Diameters of retinal arterioles and venules measured from digitised photographs of the retina taken at baseline. Measurements summarised as the arteriole: venule ratio, with a lower ratio indicating smaller arteriolar diameters. Incident hypertension, defined as systolic blood pressure≥ 140 mm Hg, diastolic blood pressure≥ 90 mm Hg, or use of antihypertensive drugs during follow up. Results: 721 participants developed hypertension over a 10 year period. Those with lower arteriole: venule ratios had a higher cumulative incidence of hypertension (incidences of 17.4% , 24.1% , 31.0% , and 45.1% , respectively, for decreasing quarters of distribution of arteriole:venule ratio). After adjustment for age and sex, participants with arteriole:venule ratios in the lowest quarter had a threefold higher risk of hypertension (odds ratio 2.95, 95% confidence interval 2.77 to 3.88) than those with ratios in the highest quarter. This association remained significant after further adjustment for baseline systolic and diastolic blood pressure and other risk factors (1.82, 1.39 to 2.40, for lowest versus highest ratio quarters). Conclusions: Narrowed retinal arterioles are associated with long term risk of hypertension, suggesting that structural alterations of the microvasculature may be linked to the development of hypertension. Obsjective: To examine the relation between diameters of the retinal arterioles and 10 year incidence of hypertension. Design: Population based prospective cohort study. Setting: Beaver Dam eye study. Participants: 2451 normotensive people aged 43 to 84 years. Main outcome measures: Diameters of retinal arterioles and venules measured from digitized photographs of the retina taken at baseline. Measurements summarised as the arteriole: venule ratio, with a lower ratio indicating smaller arteriolar diameters. Incident hypertension, defined as systolic blood pressure ≥ 140 mm Hg, diastolic blood pressure ≥ 90 mm Hg, or use of antihypertensive drugs during follow up. Results: 721 participants developed hypertension over a 10 year period. Those with lower arteriole: venule ratios had a higher cumulative incidence of hypertension (incidences of 17.4%, 24.1%, 31.0 %, and 45.1%, respectively, for decreasing quarters of distribution of arteriole: venule ratio). After adjustment for age and sex, participants with arteriole: venule ratios in the lowest quarter had a threefold higher risk of hypertension (odds ratio 2.95, 95% confidence interval 2.77 to 3.88) than those with ratios in the highest quarter. This association was significant later further adjustment for baseline systolic and diastolic blood pressure and other risk factors (1.82, 1.39 to 2.40, for as opposed to the highest ratio quarters). Conclusions: Narrowed retinal arterioles are associated with long term risk of hypertension, suggesting that structural alterations of the microvasculature may be linked to the development of hypertension.