Evidence suggests an association between obesity and oxidative stress caused by superoxide production. Since the dismutation of superoxide is catalyzed by superoxide dismutase enzymes, we tested the association between obesity and Ala16Val manganese-dependent superoxide dismutase gene (MnSOD) polymorphism. We analyzed 815 free-living community subjects (> or =60 years old) grouped into subjects who were either obese (BMI > or = 30 kg/m(2)) or non-obese (BMI < 25 kg/m(2)). Additionally, we investigated the possible interaction between the Ala16Val MnSOD gene polymorphism and obesity in the modulation of biochemical and nutritional variables. We found a positive association between MnSOD polymorphism and obesity, since higher VV frequency (28.2%) was observed in the obese group (P = 0.002, odds ratio 1.949, 95% CI: 1.223-3.008). This result was independent of sex, age, diabetes, dyslipidemia, hypertension, and metabolic syndrome. A possible biological explanation of the association described here could be a chronic state of superoxide enzyme imbalance present in VV carriers, which could affect differential metabolic pathways contributing to the obese state.