BACKGROUND In Connecticut, despite hazards of raw milk consumption, attempts to ban raw milk sales have been unsuccessful. In July 2008, 2 children experienced Escherichia coli O157-associated hemolytic uremic syndrome (HUS) after consuming raw milk purchased at a retail market and a farm (farm X). We investigated to determine the outbreak source and control measures. METHODS Confirmed cases were HUS diagnosis or E. coli O157:NM infections with isolates matching outbreak strains among patients during June to July 2008. Probable cases were diarrheal illness among farm X customers during the same period. We conducted case-control studies to determine the source of E. coli O157 exposure and assess for dose-response relation between illness and frequency of raw milk consumption. Farm X dairy practices were evaluated; stool specimens of humans and animals were cultured for E. coli O157. Staff time and laboratory and medical costs were calculated. RESULTS We identified 14 cases (7 confirmed). Five (36%) case patients required hospitalization; 3 (21%) experienced HUS. No deaths were reported. Raw milk consumption was associated with illness (P = .008); a dose-response relation was demonstrated (P = .01). Dairy practices reflected industry standards. E. coli O157:NM outbreak strains were isolated from stool specimens of 6 case patients and 1 milking cow. The total estimated outbreak cost was $413,402. CONCLUSIONS Farm X's raw milk was the outbreak source despite no violations of current raw milk regulatory standards. This outbreak resulted in substantial costs and proposed legislation to prohibit nonfarm retail sale, strengthen advisory labels, and increase raw milk testing for pathogens.