An outbreak of a single strain of Shigella sonnei resulted from the consumption of mass-produced, cold food items served on domestic and international Northwest Airlines flights. The outbreak was first detected when members of the Minnesota Vikings football team became ill. The implicated cold food items were all prepared by hand in the Northwest Airlines flight kitchen. Shigella sonnei with a different genetic pattern was isolated from one of 24 heads of leaf lettuce collected at a warehouse of a distributor to the flight kitchen. The environmental and laboratory investigations suggested that cold food items were likely contaminated by one or more infected food handlers.