BACKGROUND: There is a need to evaluate the prevalence of metabolic syndrome (MetS) diagnosed by the new Joint Interim Societies (JIS) MetS definition. The JIS definition was compared with three previous definitions to assess their ability to predict cardiovascular disease (CVD) risk.METHODS: A cross-sectional analysis of a representative sample of Greek adults (n = 9669) was performed to estimate the prevalence of MetS and CVD using the JIS vs. the three older definitions of MetS: the National Cholesterol Education Program-Adult Treatment Panel-III (NCEP-ATP-III), the International Diabetes Federation (IDF) and the American Heart Association/National Heart Lung and Blood Institute (AHA/NHLBI) definitions.RESULTS: The age-adjusted MetS prevalence was 45.7%, 43.4%, 24.5% and 26.3% (ANOVA p < 0.001) with the JIS, IDF, NCEP and AHA/NHLBI definitions. The prevalence of CVD was 11.4% in the whole study population and 17.6%, 18.3%, 23.3%, 22.6% and in subjects with MetS according to the JIS, IDF, NCEP and AHA/NHLBI definitions (ANOVA p < 0.001). The prevalence of CVD was only 10.4% (i.e., lower than in the whole study population) in subjects with MetS according to the JIS but not according to the NCEP-ATP-III and AHA/NHLBI definitions (p < 0.001 vs. subjects with MetS as defined by NCEP-ATP-III or AHA/NHLBI).CONCLUSIONS: When diagnosed according to the new JIS definition, the prevalence of MetS was high in a Greek Mediterranean cohort (nearly half of the adult population). The NCEP-ATP-III and AHA/NHLBI definitions were more predictive of CVD risk than the new JIS definition. These findings, though limited by the cross sectional analysis, may have implications regarding the choice of the definition to diagnose MetS.