Purpose: The purpose of this study was to identify an optimal definition of massive transfusion (MT)in civilian pediatric trauma. Methods: Severely injured children (age ≤ 18 years, injury severity score ≥ 25)in the Trauma Quality Improvement Program research datasets 2014–2015 that received blood products were identified. Children with traumatic brain injury and non-survivable injuries were excluded. Early mortality was defined as death within 24 h and delayed mortality as death after 24 h from hospital admission. Receiver operating curves and sensitivity and specificity analysis identified an MT threshold. Continuous variables are presented as median [IQR]. Results: Of the 270 included children, the overall mortality was 27% (N = 74). There were no differences in demographics or mechanism of injury between children that lived or died. Sensitivity and specificity for early mortality was optimized at a 4-h transfusion volume of 37 ml/kg. After controlling for other significant variables, a threshold of 37 ml/kg/4 h predicted the need for a hemorrhage control procedure (OR 8.60; 95% CI 4.25–17.42; p < 0.01)and early mortality (OR 4.24; 95% CI 1.96–9.16; p < 0.01). Conclusion: An MTP threshold of 37 mL/kg/4 h of transfused blood products predicted the need for hemorrhage control procedures and early mortality. This threshold may provide clinicians with a timely prognostic indicator, improve research methodology, and resource utilization. Type of Study: Diagnostic Test. Level of Evidence: III.