Background: Trauma severity scoring systems are routinely used to monitor trauma patient outcomes. Yet, the most accurate scoring system remains an elusive target. Objective: We aim to compare trauma severity scales (ISS, NISS, RTS, TRISS, and BIG) in multitrauma patients and investigate BIG as one of the new trauma severity scoring systems. Methods: The demographic data of the patients, vital signs, injury mechanisms, body regions exposed to trauma, final diagnosis, the injury severity scales—Injury Severity Score (ISS), New Injury Severity Score (NISS), Revised Trauma Score (RTS), base deficit, international normalized ratio, and Glasgow Coma Scale (BIG), and Trauma and Injury Severity Score (TRISS)—the length of stay in hospital, and the progress of the patients were examined. Results: A total of 426 cases were included in the study. The best performing score in determining mortality was TRISS (area under the curve [AUC]: 0.93, sensitivity 97.1% and specificity 76.7%). This was followed by the NISS, BIG, ISS, and RTS, respectively. For the prediction of intensive care unit admission, the NISS was the most successful with an AUC value of 0.81. There was a significant relationship in terms of the length of stay in all trauma scores ( p < .05). Conclusions: The most successful score in predicting mortality in trauma patients was the TRISS, whereas the NISS was the most successful in predicting intensive care unit admission. The newly developed BIG score can be used as a strong scoring method for predicting prognosis in trauma patients.