The aim of this study was to provide data on genetic hazards associated with occupational exposure to low doses of ionising radiation in nuclear medicine departments. The DNA damage in peripheral blood lymphocytes of medical staff was assessed using the chromosome aberration test. Altogether 120 subjects (60 exposed and 60 controls) participated in the study. The exposed subjects showed significantly higher frequencies of chromosome aberrations than controls. Significant inter-individual differences in DNA damage within the exposed population indicate different genome sensitivity. Age and sex were not confounding factors, while smoking increased DNA damage only in control subjects. This study suggests that chronic exposure to low doses of ionising radiation in nuclear medicine departments causes cytogenetic damage. For this reason, exposed medical personnel should minimise radiation exposure wherever possible. Our results also point to the significance of biological indicators, which provide information about the actual risk for the radiation-exposed individuals.