Objective: To examine the effects of current and past blood pressure on retina l arteriolar diameter in a general older population. Design: Cross-sectional an d longitudinal studies. Setting: Population-based cohort study of older residen ts from an area west of Sydney, Australia. Participants: Two thousand three hund red and thirty-five individuals (n=2335) (aged≥54 years) who attended the 5-y ear follow-up Blue Mountains Eye Study during 1997-99. Main outcome measures: A computer-assisted method measured vessel diameters from digitized right eye r etinal photographs. The narrowest quintile of central retinal arteriolar equival ent or arteriole-to-venule ratio (AVR) defined generalized arteriolar narrowin g. Blood pressure was measured using a mercury sphygmomanometer. Results: After simultaneous adjustment for age, sex, body mass index, smoking and current or pa st blood pressure, elevated levels of both current and past blood pressure were associated with narrower retinal arterioles <> and lower AVR <> . Generalized arteriolar narrowing was associated with both current blood pressu re <> and past blood pressure (adjusted OR 1.7, 95%CI 1.1-2.6, for the highest versus lowest quintile of past DBP). H ypertension duration or control status at baseline had no additional effect on a rteriolar diameter after adjusting for current blood pressure. Conclusions: Our data document the independent effects of both current and past blood pressure on small vessel calibre in the retina, suggesting that retinal arteriolar narrowin g may result from the cumulative effects of long-standing hypertension. Objective: To examine the effects of current and past blood pressure on retina l arteriolar diameter in a general older population. Design: Cross-sectional an d longitudinal studies. , Participants: Two thousand three hund red and thirty-five individuals (n≥235) (aged≥54 years) who attended the 5-y ear follow-up Blue Mountains Eye Study during 1997-99. Main outcome measures: A The narrowest quintile of central retinal arteriolar equival ent or arteriole-to-venule ratio (AVR) defined generalized arteriolar narrowing g. Blood pressure was measured using a mercury sphygmomanometer. Results of the computer-assisted method measured vessel diameters from digitized right eye r etinal photographs. : After simultaneous adjustment for age, sex, body mass index, smoking and current or pa st blood pressure, elevated levels of both current and past blood pressure were associated with narrower retinal arteriol es << Ptrend = 0.009 and 0.007 for current and past systolic blood pressure (SBP), respectively respectively >> and lower AVR << Ptrend = 0.0 01 and 0.0009 for current and past diastolic blood pressure (DBP), respectively >>. Generalized arteriolar narrowing was associated with both current blood pressu re << adjusted odds ratio (OR) 2.4, 95% confidence interval (CI) 1.5-3.8 for the highest versus lower quintile of current DBP >> and past blood pressure (adjusted OR 1.7, 95 % CI 1.1-2.6, for the highest versus lowest quintile of past DBP). Hypertension duration or control status at baseline had no additional effect on a rteriolar diameter after adjusting for current blood pressure. Conclusions: Our data document the independent effects of both current and past blood pressure on small vessel caliber in the retina, suggesting that retinal arteriolar narrowin g may result from the cumulative effects of long-standing hypertension.