Introduction: The BIG score is a new pediatric trauma score composed of the admission base deficit (BD), the international normalized ratio (INR) and the Glasgow Coma Scale (GCS). A score<16 identifies children with a high probability of survival following blunt trauma.The objective of this study was to measure the criterion validity of the BIG score to predict in-hospital mortality among children visiting an emergency department with blunt trauma requiring an admission to the intensive care unit. Methods: This was a retrospective cohort study performed in a single tertiary care pediatric hospital between 2008 and 2016. Participants were all children (<18 years) visiting the emergency department for a blunt trauma requiring intensive care unit admission or who died at the emergency department. All charts were reviewed by a member of the research team using a standardized report form. To insure quality of data abstraction, 10% of the charts were reviewed in duplicate by a second rater blinded to the first evaluation. The primary outcome was in-hospital mortality. Baseline demographics, initial components of the BIG score, Injury Severity Score (ISS) and disposition were extracted. The primary analysis was the association between a BIG score ≥16 and in-hospital mortality. It was calculated that the inclusion of at least 25 deaths would provide confidence intervals of +/- 0.20 for proportions in the worst-case scenario. Results: Twenty-eight children died among the 336 who met the inclusion criteria. The inter-rater agreement for data abstraction was excellent with kappa scores or intraclass correlation coefficients higher than 0.8 for all variables. Two hundred eighty-four children had information on the three components of the BIG score and they were included in the primary analysis. A BIG score ≥16 demonstrated a sensitivity of 0.93 (95%CI: 0.76-0.98) and specificity of 0.83 (95%CI 0.78-0.87) to identify mortality. Using ROC curves, the area under the curve was higher for the BIG score (0.97; 95%IC: 0.95-0.99) in comparison to the ISS (0.78; 95%IC: 0.71-0.85). Conclusion: The BIG score is an excellent predictor of survival for children visiting the emergency department following a blunt trauma.