The disaster caused by the tsunami of 26 December 2004 was one of the worst that medical systems have faced. The aim of this study was to learn about the medical response of the Thai hospitals to this disaster and to establish guidelines that will help hospitals prepare for future disasters. The Israeli Defense Forces (IDF) Home Front Command (HFC) Medical Department sent a research delegation to Thai hospitals to study: (1) pre-event hospital preparedness; (2) patient evacuation and triage; (3) personnel and equipment reinforcement; (4) modes used for alarm and recruitment of hospital personnel; (5) internal reorganization of hospitals; and (6) admission, discharge, and secondary transfer (forward management) of patients. Thai hospitals were prepared for and drilled for a general mass casualty incident (MCI) involving up to 50 casualties. However, a control system to measure the success of these drills was not identified, and Thai hospitals were not prepared to deal with the unique aspects of a tsunami or to receive thousands of victims. Modes of operation differed between provinces. In Phang Nga and Krabi, many patients were treated in the field. In Phuket, most patients were evacuated early to secondary (district) and tertiary (provincial) hospitals. Hospitals recalled staff rapidly and organized the emergency department for patient triage, treatment, and transfer if needed. Although preparedness was deficient, hospital systems performed well. Disaster management should focus on field-based first aid and triage, and rapid evacuation to secondary hospitals. Additionally, disaster management should reinforce and rely on the existing and well-trusted medical system.