A complex disaster, the Great East Japan Earthquake of March 11, 2011, consisted of a large-scale earthquake, tsunami, and nuclear accident, resulting in more than 15 000 fatalities, injuries, and missing persons and damage over a 500-km area. The entire Japanese public was profoundly affected by "3/11." The risk of radiation exposure initially delayed the medical response, prolonging the recovery efforts. Japan's representative medical organization, the Japan Medical Association (JMA), began dispatching Japan Medical Association Teams (JMATs) to affected areas beginning March 15, 2011. About 1400 JMATs comprising nearly 5500 health workers were launched. The JMA coordinated JMAT operations and cooperated in conducting postmortem examination, transporting large quantities of medical supplies, and establishing a multiorganizational council to provide health assistance to disaster survivors. Importantly, these response efforts contributed to the complete recovery of the health care system in affected areas within 3 months, and by July 15, 2011, JMATs were withdrawn. Subsequently, JMATs II have been providing long-term continuing medical support to disaster-affected areas. However, Japan is at great risk for future natural disasters because of its Pacific Rim location. Also, its rapidly aging population, uneven distribution of and shortage of medical resources in regional communities, and an overburdened public health insurance system highlight the need for a highly prepared and effective disaster response system.