Objective: To determine the prevalence of metabolic syndrome (MetS) and its components and to evaluate the relationship between this diagnosis and cardiovascular risk factors, demographic and socio-economic variables. Design: A cross-sectional study using a questionnaire including information on sociodemographic and CVD risk factors. Blood pressure, anthropometric indices, fasting glucose and lipid profile were measured. MetS was defined according to the criteria of the National Cholesterol Education Program, Adult Treatment Panel III. Setting: The whole Tunisian territory; Transition and Health Impact in North Africa (TAHINA) project. Subjects: A total of 4654 individuals (1840 men and 2814 women), aged 35 to 74 years, who participated in the Tunisian national survey. Results: The overall prevalence of MetS was 30?0 %, higher in women (36?1 %) than in men (20?6 %; P , 0?001). In both genders MetS prevalence increased significantly with age (P , 0?001), but this increase was more important in women. Multiple regression analyses showed that the odds for MetS increased significantly with urban area for both men and women (P , 0?05 and P , 0?001, respectively). The multivariate models showed also that the odds for MetS increased significantly with increasing level of education and in those with a family history of CVD for men (both P , 0?05) and after the menopausal transition for women (P , 0?05). Conclusions: The study highlights the MetS problem in a middle-income developing country. There is an urgent need for a comprehensive, integrated, population-based intervention programme to ameliorate the growing problem of MetS in Tunisians.