Both computed tomography (CTA) and conventional angiography (CCA) can provide direct visualization of the coronary arteries. The aim of the present study was to compare the radiation exposure between CTA and CCA and to search whether this amount of radiation causes significant DNA damage. Seventy-two patients who underwent CTA or CCA were enrolled prospectively. We recorded the radiation dosage that was used during the procedures and calculated the effective dose (ED). We determined the sister chromatid exchange (SCE) level from the blood samples which were drawn from the patients before and after the procedures. The change in SCE is used as the measure of DNA damage induced by the radiation. The patients in the CTA (n = 36) and CCA groups (n= 36) had similar baseline characteristics. The ED was higher in CTA examinations compared to CCA examinations (14.2 +/- 2.7 vs 6.4 +/- 3.1, P <0.001). The SCE level increased significantly after both angiography methods (P <0.001). When the change in SCE after angiography was compared, we did not find a significant difference among the groups (2.73 +/- 1.6 vs 2.54 +/- 1.22, P= NS). Although the patients who underwent CTA were exposed to a greater amount of radiation, the radiation-induced genetic damage was similar with both types of the procedures.