Clinical prediction rules are used extensively by most regionalized trauma systems to identify which patients have sustained major injuries. Because of reported high misclassification rates of some of these rules and the known global difficulty of transporting prediction rules, four such rules (the Trauma Score, the CRAMS Scale, the Revised Trauma Score, and the Prehospital Index) and two newly derived rules were statistically analyzed using a cohort of 2,434 injured patients. All rules accurately predicted mortality with a minimum sensitivity and specificity of 85%. However, not one of the rules was able accurately to identify surviving patients who had sustained major injuries. In this instance, no rule was able to achieve a sensitivity of at least 70% while achieving a specificity of 70%. These results suggest that the problem with trauma prediction rules lies in the inherent limitations of the clinical data on which they are based. In view of this, the usefulness of existing prehospital trauma predictive rules must be questioned.