Cytogenetic studies were performed in peripheral blood lymphocytes from hospital workers occupationally exposed to low doses of radiation (0.30 - 40.07mSv). The workers were divided into three groups according to their job area : 18 diagnostic radiology, 17 therapeutic radiology, and 16 nuclear medicine. The control group consisted of 49 non-radiation workers with no history of exposure to radiation. A higher percentage of cells with aberration(1.275%) was observed in the workers compared to the controls(0.677%) and the difference was statistically significant(p<0.001). The frequency of chromosomal aberration was $0.706{ imes}10^{-2}$/cell in the exposed and $0.344{ imes}10^{-2}$/cell in the control(p<0.05). Chromosomal exchange frequency was $0.083{ imes}10^{-2}$/cell in the control vs $0.245{ imes}10^{-2}$/cell in the workers. There was no evidence of significant increase of chromosome aberration related to age or to the duration of employment. The frequency of chromosomal exchange in workers of nuclear medicine was $0.313{ imes}10^{-2}$/cell, which was significantly higher than in the control($0.083{ imes}10^{-2}$/cell) or other working groups: therapeutic radiology($0.265{ imes}10^{-2}$/cell), and diagnostic radiology($0.167{ imes}10^{-2}$/cell). No dose-effect relation was found between chromosome aberration and total cumulative doses, recent 5 yr, recent 2 yr cumulative dose. But in case of last 1 yr cumulative dose, dose-dependant increase was observed when controls were considered(p<0.05). The radiation dose which workers have received was much lower than the maximum permissible dose, but there was a significant difference in the frequency of chromosome aberration between occupationally exposed workers and control. So, it is clear that chromosome aberration is a quite sensitive indicator of radiation exposure and it can be detected at very low dose level of occupational exposure.