To evaluate the processes of care and outcomes of injured patients, many different models have been devised and "Trauma and Injury Severity Score" and "A Severity Characterization of Trauma" score have been among the most widely used models. We conducted this study to determine the effectiveness of these systems of evaluation to our setting in Iran, which is substantially different from the North American trauma centers, where these models were developed. Using our data registry on trauma patients, we derived new coefficients for Trauma and Injury Severity Score and A Severity Characterization of Trauma scoring systems to calculate the probability of survival of patients. Finally, we determined the calibration and discrimination of the models by calculating the Hosmer-Lemeshow statistic and the area under the receiver operating characteristic curve. In our study, TRISS and A Severity Characterization of Trauma provided an adequate estimation of the survival probability and both models showed better discrimination in penetrating trauma. Discrimination in blunt injuries was a little lower, yet satisfactory. In pediatric patients the discrimination was also good and A Severity Characterization of Trauma had a better performance. Both models can be used reliably to predict outcome of trauma patients in our setting.