Abstract Background Computed tomography (CT) plays a central diagnostic role for trauma patients. A 16-slice multi-detector CT scanner was installed in the emergency department (ED) of Prince of Wales Hospital in December 2004. The aims of this study were to evaluate the impact of the CT scanner within the ED on trauma management and to compare the utilisation patterns of trauma CT before and after the introduction of EDCT. Methods Analysis of prospectively collected trauma registry data. All consecutive trauma cases admitted through the ED that underwent CT between June 2004 and June 2005 (6 months before and after EDCT installation) were included. A positive CT was defined as the identification (by a specialist radiologist) of a significant finding which was consistent with injury. Results There were 226 and 202 trauma patients in the 6 months before and after EDCT installation, respectively. 111 (49.1%) patients underwent CT scanning before EDCT compared with 110 (54.5%) afterwards. 72 (65%) patients had CT scans performed before admission to definitive care compared with 99 (90%) after EDCT installed ( p < 0.0001, χ 2 test). Mean time from arrival to first CT was shorter after EDCT (102 min vs. 197 min, p = 0.011). Mean trauma room length of stay increased after EDCT was implemented (106 min vs. 80 min; p < 0.001). Median time to urgent operation (<6 h) was less with EDCT (134 min before vs. 112 min after). No changes in median time to neurosurgical operation (138 min before vs. 148 min after); mean length of stay (12.8 days before vs. 12.5 days after); or mortality (8 patients before vs. 7 patients after). There were 203 scans (1.8/patient) done before EDCT compared with 226 scans (2.5/patient) after. There was no difference in the number of scans done by body region or the proportion of positive scans (32% before vs. 30% after). Logistic regression confirmed that after adjusting for injury severity and admission physiology, time to first CT was shorter ( p = 0.0307) but ED length of stay was increased ( p < 0.0001). Conclusion After the installation of EDCT, more trauma patients had CT scanning before definitive care, and scans were done sooner, with no significant increase in the number of unnecessary scans.