[en] The metabolic syndrome is strongly related to visceral obesity and associated with a high risk of cardiovascular morbidity and mortality. Since the original description of Reaven in 1988, several working definitions have been proposed, especially by the World Health Organisation in 1998-99, the National Cholesterol Education Program (NCEP-ATP III) Expert Panel in the United States in 2001 and the European Group for the Study of Insulin Resistance (EGIR) in 2002. The present paper attempts at comparing these various definitions and at reporting epidemiological data both in North America and in Europe, especially in Belgium. The prevalence is generally higher in men than in women and strongly increases with age. Overall, one may estimate that around 20% of adults have a metabolic syndrome, which should therefore be considered as an important public health problem.