In industrialized countries, studies have shown that lower socioeconomic status is generally associated with higher rates of obesity. Furthermore, poorer eating habits with insufficient intake of low energy-dense and micronutrient rich foods may increase the risk of obesity. The aim of this study was to evaluate the importance of educational, economic and dietary factors in determining obesity risk in a representative sample of the Portuguese general adult population. Study design was cross-sectional in a representative sample of Portuguese adults (20,977 women and 18,663 men). Participants were distributed in categories according to years of education (< or =4, 5-9, 10-12, and >12), income (< or =314 euros, 315-547 euros, 548-815 euros, and >815 euros), and dietary intake (vegetable soup, vegetable, fruit, bread and starchy foods). Logistic regression models were fitted to estimate the magnitude of the association between obesity and education/income, and food groups, adjusting for confounders. In women and men, the odds favouring obesity decreased with increasing education (p-value for trend <0.001) being the odds ratios, respectively, 0.19 (0.14-0.27), and 0.40 (0.30-0.54) for those having >12 years of education compared to those with < or =4 years vegetable; soup consumption also decreased the risk of obesity in both genders (odds ratios were very similar in women and men, being respectively, 0.86 and 0.89). The odds favouring obesity in women also decreased with consumption of fruit and starchy foods, being the odds ratios, respectively, 0.77 (0.64-0.92), and 0.65 (0.55-0.78). In conclusion, educational attainment and vegetable intake decreased significantly the risk of obesity in Portuguese adults from both genders; fruits and starchy foods consumption also decreased the risk of obesity in women.