The metabolic syndrome, also known as syndrome X or insulin resistance syndrome, is characterized by abdominal obesity, hyperglycemia, hypertension, hypertriglyceridemia, and reduced HDL cholesterol. In this issue of the Journal of the American Society of Nephrology, Wisse (1) describes the link between chronic inflammation of visceral adipose and the insulin resistance and pathologic features that characterize the metabolic syndrome. The prevalence of the metabolic syndrome in the United States is~47 million and rising (2), as a result of the current obesity and diabetes epidemics. Journal of the American Society of Nephrology readers are well aware that chronic kidney disease (CKD) is also increasingly common, with an estimated 8 million people in the United States with GFR Ͻ60 ml/min (Third National Health and Nutrition Examination Survey). Many aspects of the metabolic syndrome phenotype are associated with CKD, suggesting that individuals with visceral obesity are at increased risk for progressive loss of renal function.Several groups have examined the relationship between the metabolic syndrome and CKD. Hoehner et al. (3) correlated the metabolic syndrome profile and microalbuminuria in a crosssectional study of American Indians from Wisconsin and Minnesota. After stratification, individuals with three or more metabolic syndrome traits had a 2.3-fold increased odds of having microalbuminuria compared with a control group without the syndrome. Palaniappan et al. (4) and Chen et al. (5) extracted data from the Third National Health and Nutrition Examination Survey database, which contains detailed clinical information from Ͼ6000 subjects. Both studies found a statistical association between metabolic syndrome and microalbuminuria. Chen et al. also discovered a significant correlation between number of metabolic syndrome factors and GFR Ͻ60 ml/min. Individual traits that confer greatest risk were hypertension and hyperglycemia (5), which is not surprising, because both factors predispose to CKD pathogenesis and/or progression (6,7).We conclude from these reports that the metabolic syndrome is related to renal dysfunction, but a cause-and-effect relationship cannot be clearly established from these studies. Because of considerable overlap between clinical features of the metabolic syndrome and diabetes, CKD risk in individuals with the metabolic syndrome may reflect the presence of known risk factors for CKD initiation and progression-hypertension and diabetes-rather than an independent effect. One approach to identifying a distinction would be to compare the prevalence of CKD in metabolic syndrome cohorts who do or do not satisfy diagnostic criteria for diabetes. Until such a study is conducted, it is reasonable to view the renal risks and consequences of the metabolic syndrome and diabetes as indistinguishable.Some data do suggest that the metabolic syndrome may independently cause CKD. In addition to identifying BP and hyperglycemia as risks for CKD in the metabolic syndrome, Chen et al.(5) observed that...