The metabolic syndrome is a clustering of cardiovascular risk factors and is associated with an increased risk of developing diabetes, cardiovascular disease, and kidney disease. Epidemiologic studies have demonstrated differences in prevalence by age, gender, and ethnicity. The prevalence of the metabolic syndrome increases with age through the sixth decade of life among men and seventh decade among women. Most, but not all, studies reported a higher prevalence of the metabolic syndrome among women compared with men. Although the metabolic syndrome is more common among Mexican Americans compared with non-Hispanic whites and blacks, among men the metabolic syndrome is more common among non-Hispanic whites than non-Hispanic blacks; the reverse is true among women. Understanding the basic pathophysiology underlying the metabolic syndrome may help explain the age, gender, and ethnic differences in its prevalence and guide preventive and therapeutic efforts.