Metabolic syndrome X is a multifaceted syndrome, which occurs frequently in the general population. It is more common in men than in women. A large segment of the adult population of industrialized countries develops the metabolic syndrome, produced by genetic, hormonal and lifestyle factors such as obesity, physical inactivity and certain nutrient excesses. This disease is characterized by the clustering of insulin resistance and hyperinsulinemia, and is often associated with dyslipidemia (atherogenic plasma lipid profile), essential hypertension, abdominal (visceral) obesity, glucose intolerance or noninsulin-dependent diabetes mellitus and an increased risk of cardiovascular events. Abnormalities of blood coagulation (higher plasminogen activator inhibitor type 1 and fibrinogen levels), hyperuricemia and microalbuminuria have also been found in metabolic syndrome X. This review summarizes the present knowledge of abnormalities in this syndrome. Each risk factor is reviewed, and potential criteria for diagnosis and therapeutic targets are discussed. Because patients with metabolic syndrome X accumulate cardiac risk factors, they should be given special attention in terms of diagnosis and treatment.