Background: The present study assesses independent predictors of clinically important traumatic brain injury (ciTBI) in order to design a prognostic rule for identification of high risk children with mild head injury. Materials and Methods: In a retrospective cross-sectional study, 3,199 children with mild traumatic brain injury (TBI) brought to emergency ward of three hospitals in Tehran, Iran were gathered, from April 2014 to April 2016. The associations between probable predictors of ciTBI in children with mild TBI were assessed and a prediction rule for identification of high risk children in need of computed tomography (CT) scan was designed based on a stepwise multivariate logistic regression. Results: 592 (18.5%) children had ciTBI. History of loss of conciseness (odds ratio [OR]=3.0; p<0.0001), underlying disease (OR=3.6; p=0.002), Glasgow coma scale (GCS) score equal to 14 (OR=40.6; p<0.0001), altered mental status (OR=19.1; p<0.0001), need for intubation (OR=27.4; p<0.0001), presence of vomiting (OR=7.3; p=0.001), and sign of basilar skull fracture (OR=25.9; p=0.007), were the most important prognostic factors of ciTBI in children. Pediatric traumatic brain injury prognostic rule (PTBI prognostic rule) was designed based on these predictors. PTBI prognostic rule had an area under the curve of 0.93, a sensitivity of 100.0%, a specificity of 73.0% and a proper calibration (slope=0.97 and intercept=0.006) in identification of ciTBI. Conclusion: The present study showed that a few of children with mild TBI have ciTBI. Therefore, CT scans are not necessary in all of these children. Using PTBI prognostic rule can reduce the number of unnecessary CT scans.