Fairs, concerts, parades, and rallies are some of the many events that cause large numbers of people to gather in one place. Whether the event lasts a day or a week, it is evident that the people attending may require organized medical care. Most of the medical needs are minor, but cardiac arrests and other serious medical problems, including trauma, must be dealt with by the medical team. Careful planning and integration of emergency physician efforts with local hospitals and the emergency medical services system allow for an optimal delivery of health care, from the routine incident to a mass-casualty event.