Abstract: Despite comprising only 2% of all examinations,CT contributed around 20% of the collective dose to the population from diagnostic imaging.An abdominal examination in an adult with an effective dose of 10mSv has been estimated to increase the lifetime risk of fatal cancer by 1 in 2000.Children are 10 times more sensitive to the effects of radiation than middleaged adults.Girls are more sensitive than boys.Variations in CT practice,ease of using,urgency in multislice CT,unawaring of the "uncoupling effect" in CT may be contributing to increasing in radiation dose.We must train.An awareness of emerging and the implied changes in practice,with revision of protocols to take account of advances.The "as low as reasonably achievable (ALARA)" principle applies just as much to CT as it does to conventional radiography.