We tested the hypothesis that an increased body mass index was similarly associated with impaired endothelial function as measured by flow-mediated dilation in a high-risk, Hispanic population of men and women living in northern Manhattan. The association of flow-mediated dilation and body mass index was significant in women (beta -0.16 +/- 0.04, p <0.0001) but not in men (beta -0.02 +/- 0.06, p = 0.72). This is the first study to demonstrate a gender-specific difference in endothelial function associated with body mass index.