September 3, 1999, the New York State Department of Health (NYSDOH) received reports of at least 10 children hospitalized with bloody diarrhea or Escherichia coli O157:H7 infection in counties near Albany, New York. All of the children had attended the Washington County Fair, which was held August 23-29, 1999; approximately 108,000 persons attended the fair during that week. Subsequently, fair attendees infected with Campylobacter jejuni also were identified. An ongoing investigation includes heightened case-finding efforts, epidemiologic and laboratory studies, and an environmental investigation of the Washington County fairgrounds. This report presents the preliminary findings implicating contaminated well water.