Introduction: Choosing Wisely Canada has reported rates of unnecessary head computed tomography (CT) scans for low-risk mild traumatic brain injury (mTBI) patients in Ontario and Alberta ranging from 14% to 46%. Local data for Quebec is currently not available. We sought to estimate the overuse of CT scans among adults with mTBI in the emergency department (ED) of a single level II trauma center in Quebec. Methods: We performed a retrospective chart review of adults who visited the ED of Hôtel-Dieu de Lévis from 04/01/2016 to 03/31/2017. Using an administrative database (Med-GPS, Montreal), we randomly sampled ED patients aged over 18 that had an initial Glasgow Coma Scale score of 13 to 15 and had suffered from a mTBI in the last 24 hours. We excluded patients with an unclear history of trauma, a bleeding disorder/anticoagulation, a history of seizure, any acute focal neurological deficit, a return visit for reassessment of the same injury, unstable vital signs, or a pregnancy. Data was extracted by two reviewers who analyzed separate charts. They used the Canadian CT Head Rule (CCHR) to determine relevance of CT scans. Overuse was determined if a patient without any high or medium risk CCHR criteria underwent a scan. A third reviewer verified a 10% random sample of the data extraction for each primary reviewer and inter-rater reliability was assessed using the kappa statistic. Results: From the 942 eligible mTBI patients, we randomly selected 418 patient charts to review, of which 217 met all inclusion and exclusion criteria (56% were men and the mean age was 48 years old (SD = 21)). Among included patients, 101 were determined as low risk. The overuse proportion was 26% (26/101), 95% CI [18-35]. Two CT scans were assessed as abnormal, but none revealed life-threatening injuries and only one was considered clinically significant with a subdural hematoma of 9 mm. Inter-rater reliability was substantial to perfect (kappa = 0.6 and 1.0) for each primary reviewer. Conclusion: We identified head CT scan overuse in this ED. This will support local quality improvement initiatives to reduce unnecessary head CT scans for adults with mTBI.