Mass accidents do not happen often, but when they do, they cause a significant disruption in the functioning of a society with a large number of casualties and an increased percentage of deaths among the injured. The aim of the work is to present the way of organization within the emergency medical aid service in the event of a mass accident. Numerous services are involved in caring for the injured, so their mutual cooperation is important, as is the functioning within each service. Depending on the type of event, the leader of the intervention should be from the service that is responsible for the nature of the event. He is in charge of organizing the entire intervention. All the services that participate in care have their own leader who communicates with the leader of the intervention. Within the Emergency Medical Service, the triage leader and the transport leader play an important role. The triage leader is in charge of primary triage. It uses simple triage algorithms to triage the injured according to the urgency of care in four categories in the shortest possible time. After primary triage, secondary triage and treatment of the injured is in process. Only necessary measures to stabilize the injured are taken during this phase. The transport of the injured takes place based on the priority and the type of transport that is needed. During the whole treatment process, the injured must be marked with triage cards. Based on them,we can later conduct the documentation: total number of injured, number of injured by triage categories, care measures taken, method and time of transport. In order for the services to provide the best care for injured in a mass accident, the existence of unique protocols at the level of one country is necessary. In addition to protocols, education and training of employees are necessary, not only in the emergency medical service, but in all services that participate in caring for the injured. Best way to do this is shared training of employees from several departments. Only in this way can the available resources be used in the most optimal way to take care of the largest number of injured people in the best possible way and in the shortest possible time.