Long-term effects of a single low-dose radiation exposure on adult mouse brain and behavior were analyzed to determine the influence of different doses (0.063, 0.125 and 0.5 Gy), time after exposure (4, 12 and 18 months), sex and genotype (wildtype and mutant). Persistent and delayed changes were observed on behavior and hippocampal cell populations, as well as contrasting effects of the highest and lowest dose. No influence of sex was found. Impact of the mutation was significant at older age.