Results: Data were obtained from January 2006 to December 2007. Of 20 eligible months, 25,549 trauma patients presented to the emergency department. A total of 5,168 (20.2%) sustained head trauma, and 3,336 head CTs were performed with a 29.1% positive rate of substantial head injuries. The mean rate of missed head injuries among different physicians was 4.8% (range: 3.6-5.7%,p = 0.78). The monthly data were analyzed and a moderate correlation between monthly trauma volume and the decrease in positive rate of head CTs was identified (Pearson r = -0.511, p <0.05). By introducing different cut-point values of trauma volume, the threshold of trauma census in discriminating the significant decrease of positive head CTs was identified. Conclusions: The findings imply that the head CT scans might have been misused in the overcrowded setting, despite the fact that there is a standard guideline justifying its use. This phenomenon also warrants future studies focusing on the quality of care indicators regarding unnecessary examinations and the overall cost-effectiveness analysis.