A system dynamics model was developed to help hospitals assess their ability to handle surges of demand during various types of disasters.  The model represents all major flows of patients through a hospital and indicates how specific responses to a surge may ameliorate bottlenecks and their potentially harmful effects on patients.  The model was calibrated to represent a specific hospital in West Virginia and was tested under three quite different surge scenarios: a bus crash, a chemical plant leak, and a SARS outbreak. Under the difficult conditions of the SARS scenario, avoidable deaths of patients awaiting emergency care could be effectively reduced by adding reserve nursing staff not in the emergency department, as might be expected, but in the overloaded inpatient wards.  The model can help hospital planners better anticipate how patient flows may be affected by disasters, and identify best practices for maximizing the hospital’s surge capacity under such conditions.