Under physiologic conditions, insulin plays a vasculoprotective role by acting as a vasodilator through the stimulation of nitric oxide synthesis and release from the endothelium. In addition, insulin may decrease the contractile response of vascular smooth muscle cells (VSMC) to vasoactive agents by decreasing the intracellular calcium concentration i. However, in the insulin resistance syndrome, the vasodilator effect of insulin may be blunted, an abnormality that may be related to endothelial dysfunction. Insulin resistance correlates with carotid wall thickness and stiffness, but the relationship is modified by sex and ethnic factors. Insulin can act as growth factor stimulating VSMC growth in culture. Insulin-sensitizing agents are efficacious in improving the vascular pathology associated with insulin resistance.