Background: As the use of CT increases, it has raised the question for the radiation induced adverse effect. The management of blunt trauma has been influenced by the advance in the technology of CT. CT makes it possible to characterize the multiple injured patient and establish the priorities of management with more precise information. With the liberal use of CT for blunt trauma, whole body CT scanning, the-so called panscan, has often been used in trauma center to detect possible missed injuries. Within the Organization of Economic Cooperation Development (OECD) countries, South Korea has the third largest number of CT scanners per million people after Japan and Australasia. The annual number of CT examination is increasing every year. The object of this study was to assess the radiation exposure from computed tomography in multiple blunt trauma patients. Methods: This study was a retrospective cross sectional study performed for multiple blunt trauma patients visiting the OOOO Emergency Department during one year. Using data from our Hospital information system, we selected patients provided with trauma code of Korean Standard Classification of Diseases and three or more types of computed tomography at the same time in ED. The data collected by patients chart review were age, sex, initial vital signs, Glasgow coma scale (GCS), final diagnosis, injury severity score (ISS), cause of injury, mode of transportation, body location of injury, dispatch route from ED, received types CT, and the reading of CT by radiologist. Each CT conducted to patients was categorized into CT related to final diagnosis or CT unrelated to final diagnosis. Dose length product (DLP) depending on the type of CT was also examined by review of Picture Archiving and Communication System (PACS) in each patient. Total number of initial CT conducted to patients and average estimated effective dose depending type of CT were investigated. Estimated effective dose was calculated as DLP multiplied by a“ k”conversion factor. The reference for conversion factor was AAPM reports NO. 96. (9) Characteristics of CT and average effective dose unrelated to final diagnosis were also analyzed. Finally, we tried to find the factor affecting estimated effective dose. Results: 1. Clinical data of include patients and Injury details of patients. Total 110 patients were searched on the database of hospital information system during a study period. The included patients received radiographic evaluation using 16-slice CT scanner (SOMATOM Sensation 16, Siemens, Forchheim, Germany). Clinical data of included patients are shown in table 1. About one third of the patients had initial GCS score under 14 and 60 percentage of patients had ISS score under 15. The most common causes of injury were fall and motor crash injury. They occupied near half of all cause. Almost patients visited emergency department by emergency medical service (EMS) and only 13 patients visited ED via other than EMS. Head and limb were the major body location of injury. Dispatch route from ED were transferred, intensive unit, general ward, discharged home, operation and died in the order of frequency. 2. The characteristics of initial computed tomography (CT) conducted to patients. The 105 patients received total 408 CT scans initially. The main conducted types of CT were head, chest and abdomen. Estimated effective dose depending on type of CT did not differ from the levels of radiation exposure ever known. No. of patients receiving estimated effect dose over 20 mSv is 59(56.2%). About 60 percentages of total CT examinations was not associated with the final diagnosis. The patients received 2.35±1.26 (mean± standard deviation) CT scans unrelated to final diagnosis. Accordingly, average estimated effective dose due to CT unrelated to final diagnosis was 12.80±8.54 (mean±standard deviation) mSv. 3. The factors affecting the estimated effective dose. Estimated effective dose according to the sex, age, GCS, ISS, dispatched route and cause of injury was investigated. The mean values of total estimated effective dose were not different in subgroup of variables. The mean values of estimated effective dose unrelated final diagnosis were also not different in all subgroup of variables except ISS. The patients with ISS