High-frequency ultrasonographic imaging of flow-mediated dilatation (FMD) in a brachial artery, as non-invasive technique, was used for the clinical evaluation of endothelial function (EF) in 115 subjects (ages 44.19+/-12.23 (26 to 83) free of coronary heart disease or its equivalents. Our aim was to study the normative ranges for FMD in subjects of different age groups with low cardiovascular risk factors. The mean FMD was 8.23+/-4.51% (0 to 20.9). Multivariate analysis revealed that there were only two independent predictors of FMD: resting vessel diameter (r = -0.45, p<0.0001) and age (r = -0.55, p<0.0001). The multiple regression equation for this data was FMD = 25.5-0.17 x age-2.6 x resting vessel diameter. Our study demonstrates that FMD in low cardiovascular risk patients inversely correlates with age as well as brachial artery diameter. Normative ranges of FMD could be predicted for different age groups. In addition to conventional methods for the assessment of cardiovascular risk by using a population-based approach (score indexes such as SCORE, FRAMINGH, PROCAM), high-frequency ultrasonographic imaging of flow-mediated dilatation (FMD) in the brachial artery is now becoming an accepted method for the assessment of an individual patient's cardiovascular risk. Although preliminary guidelines have been published, this technique has interpretive limitations. In a study that was published earlier, the authors estimated diameter-related normal ranges of FMD. Several articles reported cut points between control and diseased groups. Data about the impact of age on FMD are also available in the literature. However, this is the first attempt to classify normal values into groups according to age and diameter.