Study Objectives: Treatment of patients following a mass casualty incident presents a complex and unique set of challenges for hospitals. Physicians and other hospital personnel must quickly mobilize to care for an influx of patients, often presenting with major injury patterns. Care for a surge of pediatric surgical and burn patients is made more difficult by the lack of large numbers of pediatric and burn care specialty centers. Non-specialty centers would likely need to manage these types of patients initially, until transfer could be arranged. We set out to characterize the surgical and burn surge capacity of a major U.S. metropolitan area, specifically assessing both regional trauma centers and community hospitals during an annual regional disaster exercise. Methods: Questionnaires were distributed to participating hospitals prior to and following the annual regional disaster exercise. The scenario was modeled after the Mumbai attacks of 2007, with terrorists spreading out across the region and attacking various targets with gunfire and explosives. These questionnaires queried the number of trauma patients hospitals estimated they could treat, number of operating rooms (ORs) and respective staff available, blood supplies on hand, as well as number and types of available surgical instruments. Results: There are a total of 62 acute care hospitals in Philadelphia, Pennsylvania, and the 4 surrounding counties, including 7 level 1 trauma centers, 2 pediatric hospitals and 1 burn center. Fifty-one of these hospitals participated in the regional exercise. There were 34 pre-exercise surveys and 26 post-exercise surveys received for analysis. On average, hospitals reported the capability to manage 4.9 adult major trauma cases acutely. However, this average number fell to less than 1 for children under the age of 8. The average was 3.8 for adult acute second and third degree burn victims, but again, the number averaged less than 1 for children under the age of 8. Thirty-five percent of participating hospitals reported inadequate blood bank surge capacity for this scenario, and 19 percent reported inadequate amounts of surgical supplies. During weekdays, hospitals were able to make an average of 12 operating rooms (ORs) available within 60 minutes of the event, but would have staffing available for an average of only 8 ORs for each hospital. During nights, weekends and holidays, those average numbers were 23 available ORs, but additional staffing for only 4 of these at 60 minutes post event. Extrapolating the average numbers to all 61 hospitals in the region yielded a total regional surge capacity of about 304 major adult trauma victims, 52 major pediatric trauma victims, 226 significant adult burn victims and 40 significant pediatric burn victims. Conclusion: While there was significant regional capacity for managing mass casualty trauma victims, staffing was a limiting factor in the number of patients who could be treated surgically within 60 minutes. Blood product shortages would also likely have an impact on mass casualty care. In addition, pediatric trauma and burn surge capacity was limited. Nights, holidays and weekend shortfalls in staffing availability also presented a challenge, given that holiday special events, sporting events and other mass gatherings occur during these times, and are potential terrorist targets.