900 children and adolescents benefit from radiation each year in France. The mean age at diagnosis is 5 years; life expectancy for the 80% of them who could cure is long, and the incidence of radiation-related acute and mainly late complications - not evaluated to date - could exceed that of adults. Dysfunction of irradiated organs and growth disorders are specific to the pediatric subpopulation. Individual radiosensitivity of children and adolescents is unknown at this time, probably with large variability depending on the age when considering the changes in metabolic functions throughout growth. These complications are largely attributable to inter individual constitutional variations of cellular response to DNA damage.