With a view to assess the independent effects of income and education on the risk of obesity we studied cross-sectional randomly selected samples of the adult population (20 y and over) living in 1996/97 in the less (northeastern) and the more (southeastern) developed region of Brazil (1971 and 2588 northeastern and 2289 and 2549 southeastern men and women, respectively). Independent effects of income and education on obesity (BMI > or = 30 kg/m(2)) were assessed through logistic regression analyses that controlled for age, ethnicity, household setting (urban or rural) and either education or income. The risk of obesity in men strongly increased with income in the two regions. The level of education did not influence the risk of male obesity in the less developed region but, in the more developed one, better-educated men had slightly less chance to be obese. In the less developed region obesity in women was strongly associated with both income (direct association) and education (inverse association). In the more developed region only the women's education influenced the risk of obesity, and the association between the two variables was inverse and strong as in the less developed region. Findings from this study reveal a scenario that is far from what has been generally admitted for the social distribution of obesity in the developing countries. They indicate that in transition societies income tends to be a risk factor for obesity, whereas education tends to be protective and that both gender and level of economic development are relevant modifiers of the influence exerted by these variables.