Analysis of peripheral blood lymphocytes in children born after the accident at the Chernobyl Nuclear Power Plant in the period from 1987 to 2004 (permanent residents of territories contaminated with radionuclides, n = 92; and children of irradiated fathers-liquidators, n = 88)) revealed increased levels of aberrant cells (ACs) and aberrations of the chromosomal type as compared to the control (P < 0.05). In three subgroups of children with different initial AC frequencies (children with high AC frequencies, > or = 3%; children with medium AC frequencies, 2%; and children with low AC frequencies, > or = 1%), the levels of aberrations of the chromosomal type are increased as compared to the control (P < 0.05). The levels of aberrant cells and chromosome aberrations (CAs) in the subgroup of children with > or = 3% frequencies significantly differ from those in the subgroup of children with > or = 1% AC frequencies. No dependence of the AC and CA frequencies on the year of birth after the Chernobyl accident was revealed. After fractional and single gamma-irradiation (137Cs) of blood in vitro in the 10-30 cGy dose range, the average CA frequencies in the first and second mitoses increased in a similar way depending on the initial AC frequencies in the children and parents. All these results suggest an individual character ofgenomic instability induced by low radiation doses and its transgenerational phenomenon in the organisms of children.