The 1994 Northridge, California, earthquake caused extensive structural damage and disrupted lives for thousands of residents. Local resources treated those initially injured. Many victims were unable or unwilling to reenter their dwellings. Record numbers of victims spent many hours at Disaster Application Centers (DACs) applying for financial assistance and other services. This created a concern for the provision of primary health care services at these centers. Under the Federal Response Plan, registered nurses, nurse practitioners, and physician assistants from the Department of Veterans Affairs treated 17,883 patients at the DACs. This report documents the injuries and illnesses sustained by the public and response workers at the DACs. The findings demonstrate that this care eased the burden on the local health care system. This article illustrates applications for estimating health services needs and demands at similar mass gatherings that might be experienced in response to catastrophic events and in U.S. military operations involving humanitarian relief missions.