Insulin resistance is associated with increased cardiovascular morbidity and mortality. The mechanism(s) underlying this association are poorly understood. Increased arterial stiffness is the main cause of the most prevalent form of hypertension, systolic hypertension. Hypertension is also commonly observed in individuals with insulin resistance. In cross-sectional epidemiological studies such as the Atherosclerosis Risk in Communities study, hyperinsulinemia was independently associated with increased arterial stiffness. Recent mechanistic studies performed in humans in vivo have suggested that increased stiffness could be yet another facet of insulin resistance. Insulin, at physiological concentrations, acutely diminishes wave reflection in the aorta in vivo. This action of insulin precedes any changes in peripheral blood flow, vascular resistance, ejection duration or heart rate, and therefore implies that insulin acutely diminishes stiffness in arteries greater than those controlling peripheral vascular resistance. This effect is blunted in insulin-resistant conditions such as obesity and type 1 diabetes. These data suggest that the inability of insulin to normally diminish arterial stiffness could provide a mechanistic link between insulin resistance and systolic hypertension.