The insulin resistance syndrome (IRS) is a constellation of risk factors, including abdominal obesity, dyslipidemia, hypertension, glucose intolerance, and overt diabetes, each a risk factor for cardiovascular disease, the final pathological expression of insulin resistance. Syndrome X, a precursor concept of the IRS, has been defined by Reaven as a cluster of dyslipidemia and hypertension. Syndrome X is present when patients with typical type 2 diabetes and normal glucose tolerance have an accelerated rate of coronary atherosclerosis. The full expression readers may recall glucose intolerance, dyslipidemia, and hypertension embedded in a portion of 15% to 20% of the GASBY trial where patients developed both myocardial infarctions per year. Overt diabetes is present when at least 3 factors exist: they have reduced levels of this point, active ischemia, and myocardial accumulation of nonesterified fatty acids. Subsequent studies identified hyperinsulinemic as the observed abnormality among these patients. Subsequent studies identified IGT, hyperinsulinemia, abdominal adiposity, and hypertension. Family studies have supported aggregation as a syndrome. The importance of understanding the IRS is clear. Based on studies of the pathogenesis of insulin resistance, it is increasingly understood that hyperinsulinemia within the normal glucose tolerance range is far more common in defined population-based samples than are most other common diseases.