Endogenous oxidative DNA damage is caused by multiple endogenous and exogenous factors. It is not completely known whether coronary angiography has an effect on DNA damage. The aim of this study was to investigate whether coronary angiography causes oxidative DNA damage. Fifty-four patients who underwent elective coronary angiography for diagnostic purpose were enrolled to the study. For each subject, the frequency of oxidative DNA damage was analyzed by using the comet assay, which is a sensitive biomarker of DNA damage, before and after diagnostic procedures. A highly significant increase of DNA damage mean score was observed in all patients after the coronary angiography procedure (p < 0.001). No significant associations were found between the change in oxidative DNA damage and dose of contrast media and radiation exposure time. A significant correlation was observed between the change of DNA damage and age, hyperlipidemia, hypertension, smoking, Gensini score index, and vitamin B,2 (r = 0.496, p < 0.001; r = 0.416, p = 0.002; r = 0.284, p = 0.038; r = 0.275, p = 0.044; r = 0.742, p < 0.001; r = -0.347, p = 0.048, respectively). The change of oxidative DNA damage was higher in patients with 3-vessel disease compared with 2-vessel disease, 1-vessel disease, and normal coronary arteries (99.6 +/- 8.4, 62.0 +/- 2.0, 43.2 8.4, 21.6 +/- 11.6 respectively; ANOVA p < 0.00 1). Multiple linear regression analysis showed that age and Gensini score index were independent predictors of the change of DNA damage (beta = 0.425, p = 0.003, beta = 0.684, p = 0.001 respectively). Our findings demonstrate that increased oxidative DNA damage in undergoing coronary angiography might be dependent on the severity of coronary artery disease and age, rather than on contrast media and radiation exposure time.