Prehospital trauma triage should permit accurate identification and transport of patients with critical injuries to trauma centers without overloading these centers with patients having minor injuries. In most trauma systems a combination of physiologic criteria (Trauma Score [TS]), mechanisms of injury (MOI), and anatomic injury (AI) are used as prehospital trauma triage criteria. The purpose of our study was to assess the predictive value of specific MOI and AI in detecting critically injured trauma victims (Injury Severity Score [ISS] of more than 15) and determine the best combination of TS, MOI, and AI that produced the lowest percentage of undertriage and overtriage. Previous studies have examined only patients triaged to trauma centers; our study included all trauma patients regardless of destination. A total of 1,473 trauma patients was evaluated and transported by the emergency medical services system and studied prospectively during a nine-week period. Prehospital TS, specific MOI and AI, and final disposition and diagnosis were determined on all patients. The ISS was calculated on all hospital admissions. A total of 97 patients had an ISS of more than 15. Three hundred forty-one (23%) had one of the specific MOI studied; 102 (6.9%) had one of the specific AI studied. Four hundred twelve patients (28%) had at least one of the study MOI or AI.(ABSTRACT TRUNCATED AT 250 WORDS)