There has been a rapid increase in the population dose from medical radiation within the last 20 years, particularly due to the increase in CT usage. Currently, about 65 million adult and 5 million pediatric CT exams are being performed in the US each year. CT-related x-ray doses are small, but very much larger than for most conventional radiological examinations. CT-related x-ray doses are large enough that there is statistically-significant epidemiological evidence of a small increase in cancer risk. Risks are larger for children. Estimated individual risks from CT are small, but the increasing population dose from increased CT usage leads to concerns about future public health problems. The various CT-based health screening applications are not yet quite ready for mass use, but will be soon, resulting in an expected further jump in CT usage. There is considerable potential, using ongoing technological developments, to reduce radiation doses per CT scan, and therefore the risks. There are significant numbers of CT scans (perhaps 1/3) which, based on medical considerations alone, either need not be done, or could reasonably be replaced with other imaging modalities. Developing and following clinical decision rules can reduce unnecessary CT usage. Communication between physician and patient about the benefits and also about the potential small risks of CT is a positive development, unlikely to reduce patient compliance.