Background. There currently is no common definitive triage scale used by both in-hospital and prehospital providers for nontraumatic transports. Objective. This study examined the ability of emergency medical services (EMS) providers to be trained in the use of a widely accepted in-hospital triage scale, the Emergency Severity Index (ESI), and to compare their performance with that of experienced emergency department (ED) registered nurses (RNs). Methods. With institutional review board approval, EMS providers, non-ED RNs with no prior exposure to the ESI, and trained ED RNs were recruited and consented to participate. Providers completed a demographic questionnaire and assigned an ESI score to 30 scenario-based questions as a pretest. This was followed by a two-hour training session with the standardized educational material published by the Agency for Healthcare Research and Quality. A second 30- item posttest was then administered. Comparisons between and within provider types were conducted with both pre- and posttest results using analysis of variance. Multivariate generalized linear regression was used to determine if provider type was predictive of preand posttest scores, when controlling for age, gender, and years of experience. Results. One hundred twenty-one providers (31 emergency medical technician–basics [EMT-Bs], 34 emergency medical technician–paramedics [EMTPs], 29 non-ED RNs, and 27 ED RNs) participated in the study. All provider types significantly improved their posttest scores from baseline (mean improvement = 18%, p < 0.05 for all groups), with mean posttest scores of 64%, 70%, 68%, and 80% for EMT-Bs, EMT-Ps, non-ED RNs, and ED RNs, respectively. The ED RNs were more likely to score higher than all other provider types on both the pre- and posttests (p < 0.001). The EMT-Bs scored significantly lower than the EMT-Ps on the posttest (p < 0.05). There was no statistically significant difference in pre- or posttest scores between the paramedics and the non-ED RNs. These differences were consistent when controlling for age, gender, and years of experience. Conclusions. All provider groups showed comparable improvement from pretest to posttest, but the posttest scores remained relatively low. Our results from scenario-based questions suggest that practical experience with the ESI may be more important than working in an emergency setting or having a specific degree (e.g., EMT vs. RN). Future research on use of this system in the field is warranted.