Visceral fat accumulation has been shown to play crucial roles in the development of obesity-related disorders such as diabetes mellitus, hyperlipidemia, and hypertension, and the so-called metabolic syndrome. Obese patients, particularly those with visceral fat accumulation, have reduced plasma levels of adiponectin, the most abundant and adipose-specific adipocytokine. A series of clinical and experimental studies has reported a link between adiponectin and obesity, the metabolic syndrome, and hypertension. Adiponectin has been recognized as a key molecule in obesity as well as in the metabolic syndrome, and a potentially promising target for the prevention and treatment of the metabolic syndrome and other diseases. This mediator may represent a novel target for the prevention and treatment of visceral obesity, the metabolic syndrome, and hypertension. This review focuses on the roles of adiponectin in the development of these diseases.