Background: Medical diagnostic procedures such as X-ray and computed Tomography (CT) scan account for considerable percent of patient's exposure to ionizing radiation. The exposure of cells to Ionization radiation results in induction of DNA damage and chromosomal aberrations. Contrast media (CM) are widely used in diagnostic radiology and CT scan. The aim of this study was to study adverse genetic effects of combined administration of non ionic contrast media and low dose X-rays in peripheral blood Lymphocytes of patients following abdominal CT scan. Materials and Methods: A total of 55 patients underwent abdominal CT scan with injection of non ionic contrast media (30 patients with omnipaque 300 mg/ml and 25 patients with visipaque 270 mg/ml) as well as 13 patients undergoing abdominal CT scan (without contrast), selected as control group, were enrolled in this study. Peripheral blood leukocytes were obtained in heparin containing tubes and cultured for the micronucleus test, or were directly used for apoptosis and DNA damage with the neutral comet assay. Results: The frequency of micronuclei, apoptosis and percentage of DNA damage was increased in most patients after the injection of contrast media, significantly different from the control group as compared with the samples obtained before and after injection of contrast media (P<0.05). Conclusion: The present study suggest that non ionic contrast media (omnipaque 300 mg/ml and visipaque 270 mg/ml) may cause a significant increase of cytogenetic damage in peripheral blood lymphocytes. This effect might be caused by the enhancement of radiation dose by CM that eventually may lead to the manifestation of ill health such as cancer.