BACKGROUND Civilian and military mass casualty incidents (MCI) are an unfortunate reality in the 21st century, but there are few situational training exercises (STX) to prepare for them. To fill this gap, we developed a MCI STX for U.S. Army Forward Surgical Teams (FST) in conjunction with the U.S. Army Trauma Training Center. METHODS After a standardized briefing, each FST has 60 minutes to unpack, setup, and organize a standard equipment cache into an emergency room, operating room, and intensive care unit. In an adjacent room, five anesthetized swine are prepared with standardized, combat-relevant injuries. The number and acuity of the total casualties are unknown to the FST and arrive in waves and without warning. A realistic combat environment is simulated by creating resource limitations, power outages, security breaches, and other stressors. The STX concludes when all casualties have died or are successfully treated. FSTs complete a teamwork self-assessment card, while staff and FST surgeons evaluate organization, resource allocation, communication, treatment, and overall performance. Feedback from each FST can be incorporated into an updated design for the next STX. RESULTS From 2003-2005, 16 FSTs have completed the STX. All FSTs have had collapses in situational triage, primary/ secondary surveys, and/or ATLS principles (basic ABCs), resulting in approximately 20% preventable deaths. CONCLUSIONS We concluded (1) a MCI can overwhelm even combat- experienced FSTs; (2) adherence to basic principles of emergency trauma care by all FST members is essential to effectively and efficiently respond to this MCI; (3) by prospectively identifying deficiencies, future military or civilian performance during an actual MCI may be improved; and (4) this MCI STX could provide a template for similar programs to develop, train, and evaluate civilian surgical disaster response teams.