Evaluation of genetic alterations in inhabitants of an area of Tamil Nadu, India, chronically exposed to highbackground radiation (HBRA), was the major purpose of the present study. A total of 216 samples (exposedinhabitants, 108; control subjects, 108) were selected based on the confirmation of radiation dose level usingthermoluminescence dosimetry (TLD). After signing a consent form, volunteers provided blood samples (5 mleach) to establish cell cultures at 52 h. One hundred complete metaphase cells from each subject were evaluatedfor karyotyping. The frequencies of chromosomal alterations (CA) were found to be higher in the exposed groupsand the aberrations predominately observed were of chromatid-type. Smoking was found to have considerableeffect on the frequency of CA in exposed subjects. With the comet assay for DNA damage, a significant increasein comet tail frequency was also observed in exposed subjects compared to controls. At present there are noradioepidemiological data regarding the cytogenetic studies in these areas. Furthermore, the Kudankulam nuclearpower plant nuclear power plant is being constructed in the same area. The study gives potentially importantinformation on the general health effects due to radiation exposure and increases people’s understanding of thehazardous nature of chronic low level natural radiation exposure. However, we may conclude that the HBRAby itself does not pose any significant risk of genetic damage as measured by conventional cytogenetic analysis.