The purpose of this study was to assess DNA damage levels in subjects with metabolic syndrome (MetS). Sixty-five subjects with MetS and 65 controls were enrolled in this study. Levels of DNA damage, total antioxidant capacity (TAC), total peroxide and oxidative stress index (OSI) were measured. We found that DNA damage levels were significantly increased [155.5 (60-264) vs. 93.2 (0-208) arbitrary units; p < 0.001] and TAC levels were significantly decreased in MetS than in control (1.34 +/- 0.27 vs. 55 +/- 0.33 mmol Trolox equivalent/l; p < 0.001). A significant falling trend in TAC levels and a significant rising trend in DNA damage values with the increase in the number of metabolic disturbances (ANOVA p < 0.001 for both) were observed. Total peroxide (30.9 +/- 4.9 vs. 21.3 +/- 2.5 mu mol H2O2/l; p < 0.001) and OSI levels [2.4 (1.3-3.8) vs. 1.4 (0.7-2.3) arbitrary units; p < 0.001] were significantly higher in the subjects with MetS than in controls. We found significant negative correlation between DNA damage and TAC levels in MetS (r = -0.656, p < 0.001) and in control (r = -0.546, p < 0.001). In multiple linear regression analysis, age, body mass index, presence of MetS and number of the componens of MetS were independent predictors of log-transformed DNA damage (p < 0.05, for all). DNA damage is increased in patients with MetS. The increase in DNA damage might be occur because of the increase in the imbalance between the production of oxidants and antioxidant defences in subjects with MetS.