On December 26, 2004, an earthquake triggered a devastating tsunami that caused an estimated 225,000 deaths in eight countries (India, Indonesia, Malaysia, Maldives, Seychelles, Somalia, Sri Lanka, and Thailand) on two continents. In Thailand, six provinces (Krabi, Phang-Nga, Phuket, Ranong, Satun, and Trang) were impacted, including prominent international tourist destinations. The Thai Ministry of Public Health (MOPH) responded with rapid mobilization of local and nonlocal clinicians, public health practitioners, and medical supplies; assessment of health-care needs; identification of the dead, injured, and missing; and active surveillance of syndromic illness. The MOPH response was augmented by technical assistance from the Thai MOPH-U.S. CDC Collaboration (TUC) and the Armed Forces Research Institute of Medical Sciences (AFRIMS), with support from the office of the World Health Organization (WHO) representative to Thailand. This report summarizes these activities. The experiences in Thailand underscore the value of written and rehearsed disaster plans, capacity for rapid mobilization, local coordination of relief activities, and active public health surveillance.