- Purpose The aim of this study was to estimate the amount of CT studies performed in the emergency department of a tertiary hospital that are not indicated by Canadian CT Head Rule (CCHR) guidelines and to analyze factors that contribute to unnecessary examinations. Methods A total of 955 brain CT examinations performed for minor head injuries were randomly retrospectively selected. Medical records were assessed for the following parameters: demographics, cause of head trauma, and referring physician's seniority and specialty. For each CT scan, it was determined whether the CT referral met the CCHR criteria. The CT interpretations of patients under 65 years of age were evaluated to assess the sensitivity and negative predictive value of the CCHR criteria. Results A total of 104 examinations (10.9%) were not indicated according to the CCHR, but in patients younger than 65 years, 104 of 279 examinations (37.3%) were not indicated. Neurologists conducted more unwarranted CT studies (odds ratio [OR], 3.5; P = .011), whereas surgeons tended to order fewer studies (OR, 0.676; P = .126). There was no statistically significant difference between the seniority of the referring physician and over-referral ( P = .181). Four-wheel motor vehicle accidents (OR, 2.789; P = .001) and a hit on the head by an object (OR, 2.843; P = .006) were associated with a higher rate of nonindicated CT examinations. The CCHR had sensitivity and negative predictive value of 100% for either brain hemorrhage or fractures. Conclusions Overuse of CT examinations for minor head injuries was demonstrated, especially in young patients, with an excess of 37.3%. Contributing factors are referring physician specialty and injury mechanism. Analysis of overuse causes can be implemented for education programs and for computerized referring protocols.