['We evaluated whether time since menopause influences the acute and chronic effect of Estradiol (E) on vascular endothelial function.', 'We studied flow-mediated dilatation (FMD) in 134 postmenopausal women (PMW) before and after acute and chronic E administration. At baseline FMD was inversely associated to time from menopause (r=-0.67, P<0.001) and age (r=-0.43, P<0.05), in exogenous estrogen naïve but not in previous users. Acute and chronic E improved endothelial function in all women. E administration improved FMD more in women within 5 years since menopause than in those with more than 5 years since menopause (76% and 74% versus 45% and 48%, acute and chronic E, respectively; P<0.05). Among women with more than 5 years since menopause acute and chronic E increased FMD more in previous E users than in nonusers (59% and 63% versus 31% and 38%, acute and chronic E, respectively; P<0.01). Multivariate analysis showed that time from menopause was a predictor of impaired FMD and of its improvement after acute and chronic E.'] Does time since menopause influence the acute and chronic effect of estrogens on endothelial function?