A complaint phoned into the local health department initiated an investigation into an Olmsted County, Minnesota, fast-food chain restaurant. This complaint was followed by four more. Epidemiologists gathered a list of other patrons and interviewed them to determine the extent of the outbreak and food histories. Stool samples were collected from cases. A total of six ill people were identified. No food was significantly associated with illness. The stool samples tested positive for Norovirus. One food worker reported illness on the day before the cases ate at the restaurant, and this worker worked on the day of exposure. This worker was determined to be the source of the outbreak.