EPI-CT is a retrospective multinational European study assessing the risk of radiation-induced cancer in a large cohort of children and adolescents exposed to diagnostic computed tomography (CT) scans. The cohort included nearly 950,000 individuals who had undergone at least one CT examination before age 22 years, identified from participating hospitals in 9 European countries: Belgium, Denmark, France, Germany, The Netherlands, Norway, Spain, Sweden and the UK. Cohort members were followed up passively through linkage with population-based cancer and mortality registries, with a median duration of incidence follow-up of 7.8 years for the whole cohort. Follow-up started at the date of the first recorded CT and ended at the earliest of: date of death; date of cancer diagnosis; or end of follow-up at the regional/national level.