BACKGROUND: Cardiovascular diseases are more frequent among the poorer social classes of the population. Studies including social and economic factors offer useful information when planning the strategy required in primary prevention. The aim of this investigation was to evaluate the association between socio-economic levels and cardiovascular risk factors in 3198 women and 3218 men aged 35-74 years enrolled for a cross sectional study within the Cardiovascular Epidemiologic Observatory, carried out in 1998 to evaluate the distribution of risk factors and the prevalence of cardiovascular risk conditions. METHODS: The level of education was used to determine the socio-economic status; the distribution of the risk factors and the prevalence of risk conditions were analyzed for the different levels of education. Models of logistic regression were used to evaluate the relation between the socio-economic status and obesity, cigarette smoking, hypertension, and hypercholesterolemia. RESULTS: A higher level of education is significantly protective against both obesity and cigarette smoking. With regard to obesity among males compared to those with a university degree the odds ratio increased to 1.6 for those with an upper secondary education diploma (95% confidence interval--CI 1.09-2.51) and to 3.5 for those without any qualification (95% CI 1.97-6.21). Among women the odds ratio increased to 3.2 (95% CI 1.81-5.81) and to 4.8 (95% CI 2.55-8.98) for the same levels of education. With regard to smoking among males compared to those with a university degree the odds ratio increased to 1.4 for those holding an upper secondary education diploma (95% CI 1.07-1.94) and to 2.3 for those without any qualification (95% CI 1.40-3.68). For men living in central or southern Italy, the odds ratio for cigarette smoking increased to 1.3 (95% CI 1.06-1.57) and to 1.5 (95% CI 1.24-1.82) and the odds ratio for hypercholesterolemia decreased to 0.8 (95% CI 0.62-0.95) and to 0.7 (95% CI 0.58-0.89); with regard to women, living in the same geographic areas the odds ratio for obesity increased to 1.3 (95% CI 1.03-1.65) and to 2.3 (95% CI 1.81-2.83). CONCLUSIONS: In primary prevention it is important to focus the attention on obesity and on smoking habits among the poorer social classes.