PURPOSE. To describe familial correlations of retinal vessel measurements. METHODS. A standardized examination and interview was administered to a population- based cohort of adults aged 43- 86 years. Blood pressure was measured, and family relationships, current smoking status, and photographs of the retina were obtained. Computer- assisted grading was done to determine central retinal arteriole (CRAE) and venule equivalents (CRVE), and the arteriole- to- venule ratio (AVR)- was computed. Familial correlations were calculated using FCOR in the SAGE software package. Analysis was done on the right eye measures for 871 sibling, 341 parent- child, 1362 cousin, 554 avuncular, and 887 spousal pairs. RESULTS. After adjustment for age, gender, mean arterial blood pressure, and current smoking status, the correlations (and 95% confidence interval) between siblings for the CRVE, CRAE,and AVR were 0.23 (0.16, 0.31), 0.20 (0.12, 0.28) and 0.13 (0.05, 0.20), respectively. Parent- child correlations were very similar, and the avuncular correlations were about half as great. The cousin correlations were about half the avuncular correlations. Spousal correlations of 0.03, 0.04, and 0.01 for CRVE, CRAJE, and AVR, respectively, were not significantly different from 0. CONCLUSIONS. Retinal vessel equivalents were more highly correlated between relatives than between unrelated individuals. The relative magnitudes of these correlations were likely the result of shared genes. Because the vessel measurements have been shown to be predictive of cardiovascular and other systemic diseases, understanding the determinants of these familial relationships could have important health benefits. METHODS. A standardized examination and interview was administered to a population-based cohort of adults aged 43-86 years. Blood pressure was measured, and family relationships, current smoking status, and photographs of The retina were obtained. Computer- assisted grading was done to determine central retinal arteriole (CRAE) and venule equivalents (CRVE), and the arteriole- to- venule ratio (AVR) - was computed. Familial correlations were calculated using FCOR in the SAGE software package. Analysis was done on the right eye measures for 871 sibling, 341 parent-child, 1362 cousin, 554 avuncular, and 887 spousal pairs. RESULTS. After adjustment for age, gender, mean arterial blood pressure, and current smoking status, The correlations (and 95% confidence interval) between siblings for the CRVE, CRAE, and AVR were 0.23 (0.16, 0.31), 0.20 (0.12, 0.28) and 0.13 (0.05, 0.20), respectively. Parent- child correlatio The cousin correlations were about half the avuncular correlations. Spousal correlations of 0.03, 0.04, and 0.01 for CRVE, CRAJE, and AVR, respectively, were not significantly different from 0 The relative magnitudes of these correlations were likely the result of shared genes. The relative magnitudes of these results between the result of shared genes. Because the vessel measurements were been shown to be predictive of cardiovascular and other systemic diseases, understanding the determinants of these familial relationships could have important health benefits.