Insulin-mediated glucose disposal varies widely in apparently healthy human beings. When insulin-resistant individuals cannot secrete enough insulin to overcome this defect, type 2 diabetes occurs. However, the ability of hyperinsulinemia to prevent gross decompensation of glucose tolerance is a mixed blessing, and insulin-resistant/hyperinsulinemic individuals are more likely to be somewhat glucose intolerant, hypertensive, and have a high plasma triglyceride and low high-density lipoprotein cholesterol concentration. These changes increase the risk of cardiovascular disease, and in 1988 these relationships were explicitly addressed and designated as comprising a Syndrome X. The fact that insulin resistance and its consequences are important cardiovascular risk factors has become widely recognized, and the importance of this syndrome was acknowledged in the report of the Adult Treatment Panel III. There has been a rapid increase in the abnormalities associated with insulin resistance/compensatory hyperinsulinemia in the 15 years since the notion of Syndrome X was introduced, and there are now almost as many components as there are names that have been given to this cluster of abnormalities. Because there is a large body of evidence that the basic abnormality leading to all of these changes is resistance to insulin-mediated glucose disposal, it seems reasonable to suggest that the cluster of abnormalities related to the defect in insulin action be designated as the Insulin Resistance Syndrome.