Smoking is the main etiological factor in the carcinogenesis process of lung cancer. But genetically defined factors such as increased levels of oxidase enzymes or chromosome aberrations have been shown to correlate with the higher possibility of contracting lung cancer among smokers. In this study, chromosome aberrations measured by micronucleus (MN) technique following in vitro irradiation were investigated in peripheral blood lymphocytes of long term smokers with or without lung cancer. Our aim is to establish the role of MN scores in identifying the individuals who might develop cancer among smokers. Twelve lung cancer patients and appropriately matching 10 healthy controls were evaluated. Spontaneous and radiation induced MN frequencies were evaluated in the two groups. An increase in the amounts of MN after 3 Gy irradiation was observed in the patient and control group when compared to spontaneous frequencies. Absolute MN frequencies as a determinant of radiosensitivity were calculated by subtraction of spontaneous aberration frequencies from the frequencies that were obtained following 3 Gy of irradiation. Absolute MN frequency range was between 0.0116 and 0.3883 with the average value of 0.1114 +/- 0.0390 (SE) for the lung cancer patients, and was between 0.0216 and 0.2291 with the average value of 0.1410 +/- 0.0234 (SE) for the controls. When the comparison was made between the absolute MN frequencies of both groups, there was no difference (p=0.159) between the two groups. In our study, it can be concluded that radiation induced MN scores in peripheral blood lymphocytes of long term smokers do not predict the risk of lung cancer.