It has been suggested that if triage criteria are to identify accurately patients with major trauma, not only physiologic status, but also anatomic site and injury mechanism must be assessed. This study examined the influence of physiologic, injury site, and injury mechanism criteria on the diagnosis of major trauma in 2,057 trauma patients. Because the Trauma Score was found to be a highly specific indicator of major trauma (98.7%), the strategy adopted for isolating the factors that minimize inappropriate triage was to determine which, alone or in combination, are the most effective in identifying patients with major trauma among those with high Trauma Scores (greater than 12). Based on this analysis, a set of triage guidelines was developed. The application of these guidelines to the study population indicated an undertriage rate of 4.1 to 6.3% and an overtriage rate of 16.8 to 21.3%, depending on the definition of major trauma.