OBJECTIVE: We sought to evaluate the performance of the Prehospital Index (PHI), the high velocity impact (HVI) criterion and emergency medical technician (EMT) judgment for the prehospital triage of injured patients. METHODS: The study population included all prehospital trauma patients transported by an emergency medical service to 2 level I trauma centres for adults. All prehospital run sheets were linked to trauma registry data. The main outcome was severe trauma, defined as death within 72 hours, admission to the intensive care unit within 24 hours or an Injury Severity Score greater than 15. We assessed sensitivity, specificity and rates of overtriage. RESULTS: Of 16,805 patients in the study population, 1113 (6.62%) had severe trauma. The combination of all 3 triage criteria (PHI score > or = 4, HVI presence and EMT judgment) performed best for identifying patients with severe trauma, with a sensitivity of 74.2% but with an overtriage rate of 85.1%. Alone, EMT judgment had the highest sensitivity and a PHI score of 4 or greater had the low est rate of overtriage. CONCLUSION: Although the combination of PHI score, HVI presence and EMT judgment offers the highest sensitivity for the identification of patients that could benefit from direct transport to a level I trauma centre, overall sensitivity remains low and over triage is high. More research is required to improve prehospital triage.