The use of Computed Tomography (CT) scans has increased 20-fold in the United States in the last three decades, which has raised concerns about the potential future cancer risks from this source of radiation exposure. The greatest concern is for children, because they are more radiosensitive than adults and the radiation doses are typically higher due to smaller body size. The United Kingdom (UK) Pediatric CT study is a record linkage study of 180,000 children who underwent CT scans before age 22, conducted by the University of Newcastle (UK) and NCI to assess whether there are cancer risks after CT scans and if so, the magnitude of the risk. The study was the first to directly suggest a link between pediatric CT scans and subsequent risk of leukemia and brain tumors. Current work includes data collection for a set of nested case-control studies to acquire individual CT films for each cancer patient and matched controls to enable more accurate dosimetry, and continued follow-up of the cohort to evaluate other cancer outcomes. The study uses state of the art dosimetry tools developed at NCI to provide organ doses from CT scans in children. An international collaboration with researchers in Canada, Israel and Australia is also planned, which will result in a dataset of approximately 800,000 children and will increase the power to examine effect modification and less common cancer outcomes. As well as providing important new information to inform public health policy on CT scan use, the study provides additional support for the linear no-threshold assumption for radiation-related cancer risks in the low-dose range.