There has been a recent move toward the adoption of five-level triage systems in the United States. However, there have been no studies in this country that have critically evaluated the use of these systems in children. The purpose of this study was to evaluate the reliability and validity of a new five-level triage system, the Soterion Rapid Triage System, for stratifying acuity levels in children under the age of 13 years. The study was conducted in a 389-bed Level II mixed adult and pediatric Trauma Center that experiences approximately 12,000 patient visits/year of children under the age of 13 years. We performed a prospective evaluation of the system's reliability using the weighted kappa statistical method (n = 117) and a retrospective evaluation of the system's validity through an analysis of all patients under the age of 13 years triaged with the system over an 8-month period (n = 7077). The system's validity was measured by in-hospital admission rate, Emergency Department length of stay, hospital charges, and Current Procedural Terminology (CPT) Codes 99281-99285. The inter-rater reliability as measured by the weighted kappa was 0.90 (95% confidence interval 0.83-0.96), with 92% exact agreement between nurses in the triage level assigned. The in-hospital admission rates for patients triaged as Level 1 Immediate-Level 5 Non-Urgent were 38%, 18%, 9%, 1.5% and 0.4%, respectively (p < 0.0001). The mean total hospital charges for each of the five triage levels were $2673, $1563, $1112, $477, and $258, respectively (p < 0.0001). Similarly, there were significant differences in the means for laboratory and pharmacy charges, Emergency Department lengths of stay, and CPT Codes. This report represents the first study in this country on the effectiveness of a five-level triage system in children. We have demonstrated that the Soterion Rapid Triage System possesses high inter-rater reliability and validity when used to triage children younger than 13 years of age.