This article describes the planning, development, and execution of a unique, decentralized, and flexible medical response capability that was developed for the 1996 Democratic National Convention in Chicago. Concerns for coordinated acts of violence, terrorism, toxicologic exposures, and logistic problems posed by the United Center prompted the development of a decentralized and flexible rapid-response plan. Contingency planning for the remote possibility of a full-scale disaster led to the additional development of a contingency mass-casualty field hospital on site. The plans for this mass-gathering response are described in considerable detail. Forty-four patient encounters across the four days of the convention were recorded, with a combination of minor injuries and potentially serious medical presentations. The 1.46 EMS encounters per 1,000 attendees at the Democratic National Convention is comparable to other utilization rates for mass gatherings in the literature. Proactive attention to comprehensive contingency planning for equipment, supplies, personnel, and organizational needs, especially when multiagency response and cooperation are required, is essential.