The long-term genetic effects in rodents inhabiting both the East Urals Radioactive Trace zone (EURT) and undisturbed territories of the Urals were investigated. The frequency of chromosome aberrations in bone marrow cells in Apodemus (S.) uralensis from radioactively contaminated sites was significantly higher than in control animals and cells with multiple chromosomal lesions were also observed. So, populations of rodents still exhibit increased level of chromosome instability despite 50 years after the radiation Kyshtym accident (over 100 generations in mice).