Participants with the metabolic syndrome are at risk of developing type 2 diabetes and coronary heart disease. The aim of this study was to determine the role of lifestyle risk factors in the development of the metabolic syndrome with particular reference to physical activity, smoking and alcohol consumption. We performed a cross sectional study of the prevalence of CVD risk factors and glucose intolerance, including type 2 diabetes involving a group of 1473 men and women were sampled from 17 general practice lists in the South of Ireland. A total of 1018 attended for screening, giving a response rate of 69%. Participants completed a detailed health and lifestyle questionnaire and provided fasting blood samples for analysis of glucose, insulin and lipids. The metabolic syndrome was defined according to the current WHO criteria. The prevalence of the metabolic syndrome was 21.0% (95% C.I. 18.7% to 24.1%). In multivariate analyses with the metabolic syndrome as the dependent variable we observed a significant, independent inverse association with physical activity level (OR=0.60; 95%CI, 0.39-0.90 for medium and OR=0.51; 95%CI, 0.28-0.93) for high level of activity relative to the low level of activity group). Ex-drinkers had a higher prevalence of the syndrome in multivariate analysis relative to occasional drinkers, (OR=2.38; 95%CI, 1.08-5.26). Prevalence of the metabolic syndrome was not significantly associated with current alcohol consumption or with smoking status. These data highlight the importance of physical inactivity in the aetiology of the metabolic syndrome.