OBJECTIVE: To develop a mathematical model for the location of trauma care resources. DATA SOURCES/STUDY SETTING: Severely injured patients queried from Maryland hospital discharge and vital statistics data. A spatial injury profile was created by parsing these patients into ZIP codes. STUDY DESIGN: The Trauma Resource Allocation Model for Ambulances and Hospitals (TRAMAH) was formulated using integer and heuristic programming. To maximize coverage of severely injured patients, trauma centers and aeromedical depots were simultaneously sited using TRAMAH. A severe injury was considered covered if at least one trauma center was sited within a time standard by ground, or if an aeromedical depot-trauma center pair was sited in such a way that the sum of the flying time from the aeromedical depot to the scene of injury plus the flying time from the scene of injury to the trauma center was within the same time standard. PRINCIPAL FINDINGS: From 1992 to 1994, 26,774 severe injuries were considered for coverage. Across Maryland, 94.8 percent of severely injured residents had access to trauma system resources within 30 minutes and 70.3 percent had access within 15 minutes. For the same number of resources as the existing Maryland Trauma System, TRAMAH achieved a coverage objective of 99.97 percent within 30 minutes. This translated into an additional 461 severely injured people covered each year. Holding in place the trauma centers of the existing system, approximately the same percentage of coverage as that of the existing system was achieved within 15 minutes by optimally locating six fewer aeromedical depots. CONCLUSIONS: TRAMAH will allow trauma systems planners to better locate their resources with respect to spatial needs and response times.