The purpose of the present study was to evaluate the predictive ability of the Prehospital Index (PHI) in identifying injury severity and to develop a trauma triage scale that incorporates, along with the PHI, a subset of time independent variables to improve the predictive ability of the PHI-based triage instrument. This study included 1,291 trauma patients treated in Montreal, Canada. The developed trauma triage protocol was based on logistic regression analysis, in which the model that predicts the data best was selected by using Bayesian information criterion. The selected regression model included the variables age, body region injured, mechanism of injury, comorbidity, and PHI. This algorithm was a substantial improvement in detecting major versus non-major injuries (major injury defined based on death, intensive care unit admission, and surgery intervention) over the PHI alone (area under the receiver operating characteristic curve: 0.76 v 0.66, P