Uniform hospital discharge abstract data from Maryland were used to examine the homogeneity of trauma-related DRGs with respect to a well-established measure of injury severity, the Injury Severity Score (ISS). Thirty DRGs were identified as including trauma cases with a wide range of severity; for each of these DRGs, ISS explains a significant amount of variation in length of stay. By applying statistical techniques similar to those used to create the original DRG groupings, these 30 DRGs were subdivided by severity and age categories to create a new set of severity-modified DRGs. The potential effects of using DRGs and modified DRGs to pay for inpatient care within the Maryland state regionalized system of trauma care were examined. Payments based on regional averages per DRG and per modified DRG were compared to actual hospital charges regulated by the state's Health Services Cost Review Commission. Using average charges per DRG as a basis of payment, approximately !1.4 million (11 percent of total hospital charges) would be shifted from trauma centers to nontrauma centers. This shift represents an 18 percent loss in revenues to trauma centers and a 30 percent gain in revenues to nontrauma centers. Using a payment system based on severity-modified DRGs, trauma centers would still experience a net loss in revenues and the nontrauma centers a net gain, but the total amount of the shift would be reduced from $11.4 million to $9.8 million. The results argue for the need to explore alternative payment systems not strictly based on current DRGs. Because of DRGs do not adequately reflect severity differences, using them to pay hospitals will create financial incentives that discourage regionalization of trauma care.