For the last few decades genome damage caused by exposure to ionizing radiation has been estimated with the use cytogenetical methods like chromosome aberration assay (CA), micronucleus assay (MN), or since recently fluorescent in situ hybridisation. However, all available studies on reliability of CA and MN to predict cancer risk are done on adult population while data concerning children are mostly related to those collected after the Chernobyl nuclear accident. After industrial nuclear accident exposures, several long-term follow-up studies have shown a higher level of genome damage and higher accumulation of radioisotopes in the skeleton of children than of adults. Similarly, rogue cells in a long-term follow-up study of exposure in industrial regions are more frequently detected in children than in adults. Additionally, is impossible to predict the transplacental impact of radioisotopes on miscarriage rate using CA in mothers. Due to its transmutation to He, tritium level in water may have a more severe impact on DNA integrity in the foetus than in adults, which results from higher mitotic rate during development. Recent studies in oncology patients using DNA microarrays identified a specific group of genes and SNPs whose expression is a signature of radiation response. These promising methods will enable researchers to detect age-related response to ionizing radiation and will give a better insight into individual cancer risk, as opposed to the group risk determined by CA and MN assays.