Study objective: Three clinical decision rules for head injuries in children (Pediatric Emergency Care Applied Research Network [PECARN], Canadian Assessment of Tomography for Childhood Head Injury [CATCH], and Children's Head Injury Algorithm for the Prediction of Important Clinical Events [CHALICE]) have been shown to have high performance accuracy. The utility of any of these in a particular setting depends on preexisting clinician accuracy. We therefore assess the accuracy of clinician practice in detecting clinically important traumatic brain injury. Methods: This was a planned secondary analysis of a prospective observational study of children younger than 18 years with head injuries at 10 Australian and New Zealand centers. In a cohort of children with mild head injuries (Glasgow Coma Scale score 13 to 15, presenting in <24 hours) we assessed physician accuracy (computed tomography [CT] obtained in emergency departments [EDs]) for the standardized outcome of clinically important traumatic brain injury and compared this with the accuracy of PECARN, CATCH, and CHALICE. Results: Of 20,137 children, 18,913 had a mild head injury. Of these patients, 1,579 (8.3%) received a CT scan during the ED visit, 160 (0.8%) had clinically important traumatic brain injury, and 24 (0.1%) underwent neurosurgery. Clinician identification of clinically important traumatic brain injury based on CT performed had a sensitivity of 158 of 160, or 98.8% (95% confidence interval [CI] 95.6% to 99.8%) and a specificity of 17,332 of 18,753, or 92.4% (95% CI 92.0% to 92.8%). Sensitivity of PECARN for children younger than 2 years was 42 of 42 (100.0%; 95% CI 91.6% to 100.0%), and for those 2 years and older, it was 117 of 118 (99.2%; 95% CI 95.4% to 100.0%); for CATCH (high/medium risk), it was 147 of 160 (91.9%; 95% CI 86.5% to 95.6%); and for CHALICE, 148 of 160 (92.5%; 95% CI 87.3% to 96.1%). Conclusion: In a setting with high clinician accuracy and a low CT rate, PECARN, CATCH, or CHALICE clinical decision rules have limited potential to increase the accuracy of detecting clinically important traumatic brain injury and may increase the CT rate.