The amount of radiation that people are receiving from medical sources is increasing, and this includes children. It is difficult to show directly that radiation doses from CT lead to cancer. However, good data from other sources of exposure show that there are increased cancers in people who have been exposed to radiation at levels that can be encountered by patients undergoing CT scans. This is particularly important in children, whose tissues are more radiosensitive, who receive a larger effective dose for a given level of radiation, and who have a longer time to develop cancers resulting from radiation exposure. For any one person, the lifetime risk of death from cancer is about 1 in 5. While estimates vary, for a child undergoing a single CT of the abdomen and pelvis increases that risk by 1 in 1,000. The risk is cumulative, however, and each subsequent CT scan will increase the risk accordingly. While for any one individual the increased risk is very small, given the large number of CT scans performed the risk to the population as a whole is much larger.