CT has been used to save many patients’ lives and the demand for CT is still increasing. At the same time, there has been increasing concern of the probability of cancer induction by CT radiation. It is necessary for everyone involved in CT scanning, particularly physicians who have to communicate with patients when planning a CT scan, to have a basic knowledge of the CT radiation dose and its potential adverse effects. We have undertaken a systematic review of the literatures to document the radiation dose from CT, the lifetime cancer risk from CT exposure, CT dose parameters, the internationnal CT diagnostic reference levels, and the use and limitation of the CT effective dose. In addition, we conducted a brief survey of the use of CT scan in some university hospitals in Thailand and estimated current CT doses at these hospitals. Our review and survey suggests that CT scanning provides a great benefit in medicine but it also becomes the major source of X-ray exposure. Radiation doses from a CT scan are much higher than most conventional radiographic procedures. This raises concerns about the carcinogenic potentials. We encourage every CT unit to adhere to the International Guidelines of CT dose parameter references. Our preliminary survey from some university hospitals in Thailand revealed that CT radiation doses are within acceptable standard ranges. However, the justification for utilization of CT scans should also be required and monitored. The importance of adequate communication between attending physician and consulting radiologist is stressed.