The prevalence of the metabolic syndrome using either the National Cholesterol Education Program Adult Treatment Panel III or World Health Organization definitions is high and likely increasing among US adults. The large number of people with the metabolic syndrome has serious implications for public health and clinical practice. The associated costs are likely to be substantial. Future increases in the incidence of cardiovascular disease and diabetes could occur. Because patients with the metabolic syndrome will make up a large proportion of the practices of health care professionals, health care professionals must be knowledgeable about the metabolic syndrome and be prepared to diagnose it.