To compare accuracy of a computer simulation in predicting patient flow during a mass casualty incident with that of a real-time virtual live exercise (VLE), 136 simulated victims of a mass casualty incident, the Disastermed.ca database, was used as input into a computer simulation which was developed using the SimProcess (CACI Products, San Diego CA) platform to represent the Emergency Department of the University of Alberta Hospital. The VLE was performed using a training version of the hospital's Emergency Department Information System (HASS/iSoft, Branbury, UK). Prospective data collection was performed to compare the results of the computer simulation to that of the VLE.