This talk will review the historical evidence for the purported impacts of male and female sex hormones on the vasculature in humans, including effects on macro- and micro-vascular function and health. Direct comparisons between the sexes, in terms of in vivo measures of arterial size and function, will be provided from a large sample of 950 asymptomatic and healthy, pre- and post-pubertal children (6-18 yrs). These data will be compared to sex differences apparent in 180 adults in whom the modulating impacts of fitness, BMI and cardiovascular risk factors are also be addressed. Finally, the results of two recent laboratory studies from our team, in which younger men and women were recruited and directly compared to older cohorts, will be presented. Although based on small sample sizes, these studies suggest that differences exist between men and women in terms of the impact of age on arterial function (flow-mediated dilation FMD and glyceryl trinitrate GTN) and structure (arterial diameter, wall thickness and wall:lumen ratio) and that cardiorespiratory fitness modulates these differences. The impact of exercise training in older sedentary men and women will also be considered, with an emphasis on the degree to which age-related changes can be ameliorated in both sexes. Ultimately, this talk will highlight the paucity of high quality and compelling evidence regarding the fundamental impact, in humans, of sex differences on arterial function and structure as people age.