Aortic Windkessel function is thought to represent a potential cardiovascular risk factor. As an indicator for the function, we have recently introduced the decay index (DI). DI is the coefficient of an exponential function applied to the postpeak portion of internal carotid artery Doppler waveform, and is inversely associated with the function. This study compares DI with age, gender and traditional cardiovascular risk factors in 220 apparently healthy volunteers (59 +/- 16 years). DI increased linearly with age (r = 0.51, p < 0.001), and was higher in women than in men at all ages (p < 0.001). Also, DI was positively associated with systolic blood pressure (beta = 0.17, p < 0.01) and diabetic medication (beta = 0.14, p < 0.05), independent of age (beta = 0.49, p < 0.0001), gender (beta = 0.27, p < 0.0001) and other traditional cardiovascular risk factors (model r(2) = 0.36). Based on the present results, the Windkessel function as assessed by DI declines with age and is lower in women. However, the associations with cardiovascular risk factors need to be established on a larger sample at higher cardiovascular risk.