The Trauma Score (TS) is a physiologic measure of injury severity that correlates with patient outcome. Application of the TS has shown that it is useful for patient triage, for predicting patient outcome, and as a means of normalizing for case mix when comparing prehospital care and transport modalities. Our study explored the interrater reliability of assessments of TS variables that were made by emergency medical technicians and paramedics during the prehospital phase. Results showed that 95.3% of the assessments made by prehospital personnel agreed with those made by a highly-trained nurse observer, despite slight variations in assessment techniques. The results have implications for prehospital field use of the TS.