Evidence on aortic root dimension for predicting cardiovascular morbidity and mortality is inconclusive. This cohort study sought to characterize the predictive power of aortic root dimension on cardiovascular morbidity and mortality in an ethnic Chinese population. We recruited 1,851 participants in the Chin-Shan Community Cardiovascular Cohort (CCCC) study who had received echocardiography without previous cardiovascular events. Aortic root dimension was measured by M-mode echocardiography and indexed by body surface area to obtain aortic root dimension index (AOI). The end points were all-cause death and incident cardiovascular events including coronary heart disease and stroke over a median follow-up of 11.9 years. Although tertiles of AOI was associated with an increased risk of cardiovascular events and all-cause death in univariate analysis, the significance diminished after adjusting for age variable (P for trend = 0.11 for cardiovascular events; P for trend = 0.23 for all-cause death). In subgroup analysis, we found a significant association between tertiles of AOI and risk of all-cause death in the final multivariate Cox regression model in adults <65 years. The adjusted relative risk was 1.88 (95% CI, 1.04 to 3.40) in participants in the upper tertile of AOI compared with participants in the lower tertile (P for trend = 0.037). In adults > or = 65 years, tertile of AOI was not associated with all-cause death (P for trend = 0.14). Tertiles of AOI was not associated with cardiovascular events throughout this study. Our study showed a significant association between AOI and all-cause death in adults <65 years in an ethnic Chinese population. (Echocardiography 2010;27:487-495).