The metabolic syndrome is a clustering of abnormalities that confers an increased risk of cardiovascular disease and type 2 diabetes. Five organizations have proposed definitions of the syndrome. Despite differences in specific criteria among the definitions, there is agreement that the major characteristics of the syndrome include central obesity (except in one definition), elevated blood pressure, dyslipidemia, and impaired glucose metabolism or insulin resistance. Large variations exist in the prevalence of the metabolic syndrome across countries and regions, ethnic groups, and gender. The prevalence is high and increasing, particularly in North and South American countries. The high prevalence, combined with the large number of people at risk for cardiovascular disease, type 2 diabetes, and other related disorders, suggests that the metabolic syndrome may present a major worldwide public health challenge in future.