BACKGROUND: Individuals with the metabolic syndrome (MS) are at high risk for coronary heart disease. In this study, we evaluated the levels of inflammatory, lipidaemic and glycaemic control markers in subjects with and without MS, as given by different definitions. METHODS: During 2001-2002, we randomly enrolled 1,514 men (18-87 years old) and 1,528 women (18-89 years old), without any clinical evidence of cardiovascular disease, from the Attica area, Greece. Among several variables, we also measured inflammatory markers, total antioxidant capacity, glucose and insulin levels and various lipids. MS was defined according to either the National Cholesterol Education Program Adult Treatment Panel (NCEP ATP) III criteria or the International Diabetes Federation (IDF) Epidemiology Task Force group. In all the analyses, subjects with diabetes were excluded. RESULTS: The prevalence of the MS was 17.9% according to the NCEP definition and 48.9% according to the IDF definition (p < 0.001). The prevalence of MS was higher in men compared with women according to both definitions (p for gender differences <0.001). Moreover, 3.9% of the total study sample fulfilled only the NCEP criteria, but not the IDF, while 38.6% fulfilled only the IDF criteria. Subjects who were defined as having MS using the IDF criteria were younger, had higher body mass index, C-reactive protein, fibrinogen, tumour necrosis factor-alpha levels, total antioxidant capacity and lower glucose and insulin levels. CONCLUSIONS: Prevalence of the MS is very high among Greek adults when the IDF definition is used, while it is still considerable when we adopt the NCEP criteria. It is evident that subjects who fulfilled the IDF criteria showed increased levels of inflammatory markers compared with those who fulfilled the NCEP ATP III criteria.