The metabolic syndrome comprises a cluster of cardiometabolic risk factors, with insulin resistance and adiposity as its central features. Identifying individuals with metabolic syndrome is important due to its association with an increased risk of coronary heart disease and type 2 diabetes mellitus. Attention has focused on the visceral adipose tissue production of cytokines (adipokines) in metabolic syndrome and type 2 diabetes mellitus, as the levels of the anti-inflammatory adipokine adiponectin are decreased, while proinflammatory cytokines are elevated, creating a proinflammatory state associated with insulin resistance and endothelial dysfunction. In this review, we will give special attention to the role of the leptin/adiponectin ratio. We have previously demonstrated that in individuals with severe coronary artery disease, abdominal obesity was uniquely related to decreased plasma concentrations of adiponectin and increased leptin levels. Leptin/adiponectin imbalance was associated with increased waist circumference and a decreased vascular response to acetylcholine and increased vasoconstriction due to angiotensin II. Leptin and adiponectin have opposite effects on subclinical inflammation and insulin resistance. Leptin upregulates proinflammatory cytokines such as tumor necrosis factor-α and interleukin-6; these are associated with insulin resistance and type 2 diabetes mellitus. In contrast, adiponectin has anti-inflammatory properties and downregulates the expression and release of a number of proinflammatory immune mediators. Therefore, it appears that interactions between angiotensin II and leptin/adiponectin imbalance may be important mediators of the elevated risk of developing type 2 diabetes mellitus and cardiovascular diseases associated with abdominal obesity.