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Background: Sex is a major determinant of cardiovascular disease (CVD). Endogenous sex hormones exert a variety of effects on the vascular endothelium, and changes in sex hormone levels after menopause may play a role in CVD risk in women. We hypothesized that a more androgenic sex hormone profile among post-menopausal women, but not among men, would be associated with reduced blood flow-mediated vasodilation (FMD) of the brachial artery, a marker of worse endothelial function.Methods: We examined 1396 post-menopausal women and 1707 men participating in MESA, who were free of clinical CVD at baseline. Sex hormone levels [total testosterone (T), sex hormone binding globulin (SHBG), estradiol (E2)] were measured at Exam 1 (2000-02); free T and T/E2 ratio were calculated. FMD was measured by high-resolution ultrasound. Using multivariable adjusted Poisson and linear regression methods, we tested the cross-sectional associations of sex hormones (log transformed) with FMD.Results: The mean age of men and women was 61 and 64 years, respectively. Of women, 34% were using hormone therapy (HT). Among women, after adjusting for demographics, CVD risk factors, and HT use, higher SHBG was associated with higher FMD, whereas higher free T was associated with lower FMD (Table, Model 2). In women, when examining the “best FMD response” (top decile vs. bottom 9 deciles), higher E2 was positively associated with a prevalent best response, whereas higher free T was inversely associated. Among men, a higher T/E2 ratio was marginally associated with lower FMD.Conclusion: The association between sex hormones and FMD differs in men and women. Higher E2 and SHBG and lower free T levels were associated with better FMD in post-menopausal women but not in men. Higher T/E2 ratio was associated with lower FMD in men. Further studies are needed to assess longitudinal changes in sex hormone levels and their association with vascular aging. Sex hormone levels may help identify individuals at increased CVD risk who may benefit from other risk reduction strategies.