Endothelial vasodilator dysfunction and carotid intima-media thickening (IMT) are 2 indicators of subclinical cardiovascular disease. We examined their correlation and interaction with risk factors in a large, community-based cohort of young adults. As part of the longitudinal Cardiovascular Risk in Young Finns Study, we measured endothelium-dependent brachial artery flow-mediated dilatation (FMD) and carotid artery IMT by ultrasound in 2109 healthy adults aged 24 to 39 years. FMD was inversely associated with IMT (P< or =0.001) in a multivariate model adjusted for age, sex, brachial vessel size, and several risk variables. The subjects with age- and sex-specific FMD values in the extreme deciles were classified into groups of impaired (n=204, FMD=1.1+/-1.4%, mean+/-SD) and enhanced (n=204, FMD=16.3+/-2.9%) FMD response. The number of risk factors was correlated with increased IMT in subjects with an impaired FMD response (P<0.05) but not in subjects with an enhanced FMD response (P>0.2). Brachial FMD is inversely associated with carotid IMT. The number of risk factors in young adults is correlated with increased IMT in subjects with evidence of endothelial dysfunction, but not in subjects with preserved endothelial function. These observations suggest that endothelial dysfunction is an early event in atherosclerosis and that the status of systemic endothelial function may modify the association between risk factors and atherosclerosis.