In the present study, uranium mine-workers in the Stepnogorsk mining-milling complex in Northern Kazakhstan were investigated for the expression of chromosome aberrations and for genetic factors that can modify the exposure-related expression of chromosome damage. From our interview of volunteers, 100 qualified workers occupationally exposed to uranium and 56 control people who had not been exposed to radiation or other hazardous agents were selected. The workers were subdivided into 3 groups according to the duration of exposure: group I – 1-10 years, group II – 11-20 years, group III – 21-25 years. Our data show that workers in all three exposure groups had higher frequencies of chromosome aberrations than the control group. Uranium-exposed workers who had inherited the null GSTM1 and/or GSTT1 genotypes had a significant increase in the frequency of chromosome aberrations compared with those who had the intact GSTM1 and GSTT1 genes for the different group of workers. Our study suggests that uranium mine-workers in Northern Kazakhstan have excessive exposure that can cause an increased risk for health consequences such as cancer. In addition, GSTM1 and/or GSTT1 null genetically susceptible individuals may have higher health risk.