Since 1971 a cooperative effort has existed between the Health Effects Research Laboratory, US Environmental Protection Agency (USEPA), in Cincinnati, Ohio, and the Center for Disease Control (CDC) in Atlanta, Ga., for the purposes of investigating, documenting, and reporting waterborne disease outbreaks in the United States. Local and state health departments investigate waterborne disease outbreaks and, at times, request assistance from CDC and USEPA. As part of the reporting system, state epidemiologists and engineers in state water supply organizations cooperate in providing data on waterborne outbreaks to these two agencies annually. This report summarizes data reported to USEPA and CDC on waterborne disease outbreaks during 1971–1978.