Introduction: The PECARN head CT scan rule helps to identify children at risk of clinically important Traumatic Brain Injury (ciTBI) but many children fall in a grey zone while applying the rule (observation vs. CT scan). The C-3PO rule identifies children at risk of skull fracture. The Ste-Justine Head Trauma pathway comprises both rules for the management of all children younger than two years who suffered a head trauma. The primary objective of this study was to measure the capacity of the Ste-Justine Head Trauma pathway to identify children with ciTBI. Methods: This was a retrospective study of all children younger than two years old who visited a university affiliated pediatric emergency department (ED) for a head trauma between Sept. 2013 and Aug. 2015. Participants were all patients admitted for a head trauma and a randomly selected sample of 5% of non-admitted patients. Independent variables of the algorithm were recorded for each patient. The primary outcome was the presence of a ciTBI defined by any of the following secondary to TBI: death, neurosurgery, intubation of more than 24 hours or hospitalization for more than one night. Participants were identified using the computerized database of the ED and all charts were reviewed using a standardized report form. The primary analysis was the proportion of children with ciTBI accurately identified using the pathway. A secondary analysis was to compare the performance of the pathway in comparison to the PECARN rule alone. Results: During the study period a total of 2,258 children were seen in the ED for head trauma. The charts of all hospitalized (n=100) and a sample (n= 101) of non-hospitalized children were reviewed. A ciTBI was found in 26 participants (3 neurosurgical interventions, 4 intubated and 26 admitted > one night). Among them, 18 were classified at high risk, 7 at moderate risk and 1 at low risk according to the clinical pathway. Using the PECARN rule alone would have classified 17 at high risk, 5 at moderate risk and 4 at low risk. Using the pathway to the entire population would yield the following risk of cTBI: High-risk: 25%; moderate risk: 1%; low risk < 0.1%. Conclusion: The Ste-Justine Head Trauma pathway effectively identifies children younger than two years at risk of ciTBI following head trauma while triaging effectively children at low risk. The pathway is more sensitive than the PECARN rule to identify children at risk of ciTBI.