Objective: To examine the relation between diameters of the re tinal arterioles and 10 year incidence of hypertension.Design: Population based prospective coho rt 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. Mea surements summarised as the arteriole: venule ratio, with a lower ratio indicati ng smaller arteriolar diameters. Incident hypertension, defined as systolic bloo d pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or use of antihyper tensive drugs during follow up. Results: 721 participants developed hypertension over a 10 year period. Those with lower arteriole: venule ratios had a higher c umulative incidence of hypertension (incidences of 17.4%, 24.1%, 31.0%, and 4 5.1%, respectively, for decreasing quarters of distribution of arteriole:venule ratio). After adjustment for age and sex, participants with arteriole:venule ra tios in the lowest quarter had a threefold higher risk of hypertension (odds rat io 2.95, 95%confidence interval 2.77 to 3.88) than those with ratios in the hig hest 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 ret inal arterioles are associated with long term risk of hypertension, suggesting t hat structural alterations of the microvasculature may be linked to the developm ent of hypertension. Objective: To examine the relation between diameters of the reinal arterioles and 10 year incidence of hypertension. Design: Population based prospective coho rt study. Settings: Beaver Dam eye study. Participants: 2451 normotensive people aged 43 to 84 years. : Diameters of retinal arterioles and venules measured from digitized photographs of the retina taken at baseline. Mea surements summarised as the arteriole: venule ratio, with a lower ratio indicati ng smaller arteriolar diameters. Incident hypertension, defined as systolic bloo d pressure ≥ 140 mm Hg, diastolic blood pressure ≥90 mm Hg, or use of antihyper tensive drugs during follow up. Results: 721 participants developed hypertension over a 10 year period. Those with lower arteriole: venule ratios had a higher c umulative incidence of hypertension (incidences of 17.4%, 24.1%, 31.0%, and 4 5.1%, respectively, for decreasing quarters of distribution of arteriole: venule ratio). After adjustment for age an d sex, participants with arteriole: venule ra tios in the lowest quarter had a threefold higher risk of hypertension (odds rat io 2.95, 95% confidence interval 2.77 to 3.88) than those with ratios in the hig hest quarter. further adjustment for baseline systolic and diastolic blood pressure and other risk factors (1.82, 1.39 to 2.40, for as highest versus quarters). Conclusions: Narrowed ret inal arterioles are associated with long term risk of hypertension, suggesting t hat structural alterations of the microvasculature may be linked to the developm ent of hypertension.