The implementation of a contemporary comprehensive Emergency Medical Services System (EMSS) has resulted in a change in the method and character of initial response to and overall management of disaster situations. The focus of patient assessment and care responsibilities has shifted from the hospital to the scene of the disaster where triage, evaluation, and medical management of multiple casualties occur. New developments in the organization of EMS Systems dictate that new approaches to disaster planning and preparedness are essential in order to implement the current concepts of emergency medical services. The Boston Emergency Medical Services System has instituted a modern disaster plan which includes principles of hospital categorization, specialty center designation, hospital point-of-entry plans, multihospital resource determination (bed availability), scene triage, patient staging, patient transfer procedures, air evacuation, use of sophisticated telecommunications systems, and regionalization of resources. The activities are all centrally coordinated through one Resource Trauma Center, utilizing a centralized communications center with central medical emergency direction (CMED) capabilities.Four disasters are reviewed: a courthouse bombing with 20 victims, to which there was a 2.5 minute response time, and for which four hospitals were utilized; a factory explosion with 13 critically burned victims air and ground transported to four definitive regional specialty centers; two simultaneous hotel fires with 73 victims who required transport to six hospitals after being treated in on-scene triage areas; and the crash of a jetliner carrying 208 people, 33 of whom required transport to seven hospitals.