Purpose: We compared the Korean Triage and Acuity Scale (KTAS), Injury Severity Score (ISS), and Revised Trauma Score (RTS) determined the validity of KTAS for classifying trauma patients. Methods: A retrospective chart review of 10,865 trauma patients (aged ≥15 years) who visited a single regional trauma and emergency medical center from January 1, 2016, to December 31, 2020, was conducted. Data were collected from the Korean Trauma Data Bank. Based on KTAS classification, the rates of intensive care unit admission, surgery and intervention, transfusion, emergency room (ER) and hospital mortality, and ER stay time were investigated. Data were analyzed using Chi-square test, Pearson's correlation coefficient, receiver operating characteristic curve, and area under the ROC curve. Results: In the KTAS, severe trauma patients (ISS ≥16) were classified as Level 1 (79.6%), 2 (44.8%), 3 (15.5%), 4 (4.0%) and 5 (7.6%). The following were the predictive powers of KTAS, ISS, and RTS for different parameters: surgery and intervention rate, KTAS (.71), ISS (.70), and RTS (.63); transfusion rate within 4h, KTAS (.82), ISS (.82), and RTS (.74); ER stay time within 90 min, KTAS (.72), ISS (.62), and RTS (.56); and ER mortality, KTAS (.84), ISS (.72), and RTS (.88). These findings were statistically significant (p<.001). The sensitivity and specificity of KTAS for trauma patients were .88 (.87~.90), and .38 (.37~.39), respectively. Conclusion: KTAS is a useful classification system that can predict the clinical outcomes of patients with trauma, and effectively triage acutely ill trauma patients, thus provide appropriate treatment.