OBJECTIVE: The rapid increase in obesity rates over recent years suggest that cultural and societal influences are affecting the adjustment in the energy balance equation in addition to other physiopathological or genetic determinants. Therefore, a pan-EU study was carried out to explore the influence of sociodemographic factors as well as some attitudes (smoking and exercise) on the prevalence of obesity in the adult population of all 15 member states of the EU. DESIGN: Overall, a sample of 15,239 individuals aged 15 years and upwards in the EU completed the questionnaire. Subject selection was quota-controlled to make the sample nationally representative following a multistage stratified cluster sampling. Self-reported height and weight were used to calculate body mass index (BMI). RESULTS: From the EU average results, it can be seen that only about half of the EU population (48%) is within the normal weight range, while the obesity (BMI > or = 30 kg m(-2)) prevalence was about 10% in the EU and the overweight prevalence was 36.6% and 25.6% among men and women, respectively. UK subjects had the highest prevalence of obesity (12%), while Italians, French and Swedes had the lowest levels of obesity (about 7%). Concerning age and social class interactions, logistic regression analysis showed that high social class and younger individuals in all groups had a lower odds ratio for obesity prevalence. People with a higher level of education are less likely to be obese, while the interaction between educational levels and obesity was different for men and women. A low participation in various leisure-time physical activities, the lack of interest (precontemplation) in being involved in exercise/physical activity and the increasing number of hours sitting down at work appear to be predictors of obesity. Single individuals were less prone to become obese than couples or widowed/divorced people. Finally, smoking status was statistically linked to the prevalence of obesity, since non-smokers or ex-smokers for more than 1 year presented a higher tendency for a BMI > 30. CONCLUSIONS: This survey confirms that a priority area for health intervention aimed at preventing the development of obesity should be to increase levels of physical activity, although the approach will depend on the population, especially with respect to educational and socioeconomic aspects.