Potential terrorist attacks and the possibility of naturally occurring disease outbreaks have raised concerns about the "surge capacity" of the nation's health care systems to respond to mass casualty events. GAO identified four key components of preparing for medical surge: (1) increasing hospital capacity, (2) identifying alternate care sites, (3) registering medical volunteers, and (4) planning for altering established standards of care. The Department of Health and Human Services (HHS) is the primary agency for hospital preparedness, including medical surge.This is an edited and excerpted edition.