Customers eating at the Country Cottage Restaurant in Locust Grove, Oklahoma, between August 15 and August 24, 2008, became ill with E. coli O111. The exact mode of spread within the restaurant was never established, however the epidemiological analysis suggested that there had been ongoing foodborne transmission until the restaurant was closed by health officials on August 25. E.coli O111 was not isolated from any food or environmental surface in the restaurant. It was uncertain how the contamination entered the restaurant. Five employees had reported consistent illness symptoms prior to, or concurrent with, the outbreak. Stool samples collected from ill employees failed to show the presence of E .coli O111. A private well on the premises had been accessed and used to supply water to the restaurant just prior to the initiation of the outbreak. Water sample testing showed the presence of total and fecal coliforms. Numerous E. coli were cultured from the well water samples, but none were found to be Shiga toxin-producing or typed as E. coli O111. Twenty six persons developed hemolytic uremic syndrome, a serious kidney and blood complication of toxigenic E. coli infections.