The association between elevated values of reactive oxygen species and a decreased antioxidant capacity defines oxidative stress. Oxidative stress involvement is blamed in many diseases, including obesity. We evaluated oxidative stress levels by FORT (Free Oxygen Radical Testing � reactive oxygen species levels) and FORD (Free Oxygen Radical Defence � antioxidant capacity value) assays in obese subjects vs. controls. FORT values were high and FORD values were low in obese patients vs. controls, notably in obese subjects with comorbidities (diabetes, hypertension, dyslipidaemia, coronary heart disease, anaemia, hepatic steatosis). We found positive correlations between FORT values and total cholesterol, uric acid, triglycerides, LDL, body mass index, HDL/total cholesterol ratio, and negative correlations between FORT and age, HDL. FORD levels correlated oppositely to FORT. Our results suggest that obesity and oxidative stress are linked.