The purpose of this study was to measure the predictive power of Acute Physiology and Chronic Health Evaluation (APACHE II) with respect to mortality in a group of seriously injured patients and to compare this predictive power with that of the Trauma Score (TS) and the Injury Severity Score (ISS). Six hundred ninety-one helicopter-transported patients were studied. Individual logistic regressions demonstrated that all three scores had significant predictive power when considered individually (TS chi 2 = 136, p less than .0001; APACHE II chi 2 = 171, p less than .0001; ISS chi 2 = 109, p less than .0001). In addition, each severity score added significantly to the predictive power in a stepwise logistic regression (TS chi 2 = 15, p less than .0001; APACHE II chi 2 = 45, p less than .0001; ISS chi 2 = 15, p less than .0001). Areas under the receiver operating curves for the three scores were not significantly different (TS 0.8116, SD 0.0245; APACHE II 0.8515, SD 0.0204; ISS 0.7967; SD 0.0223). APACHE II is a good predictor of mortality, and its predictive power is complemented by TS and ISS.