In November, 1999, seven residents of a Pennsylvania retirement facility were hospitalized with E. coli O157:H7 infections. An investigation determined the outbreak was associated with eating romaine lettuce that had been prepared in one of the facility’s three kitchens. In this kitchen, the lettuce was washed by soaking it briefly in water. Another kitchen in the facility received the same romaine lettuce, during the same time period, but rinsed it in a colander. No illnesses were associated with lettuce from this kitchen. The E. coli O157:H7 strain was compared with E. coli O157:H7 strains identified and posted on the PulseNet system. The strain matched a strain that had been implicated in an outbreak in Oregon. The risk of illness in the Oregon outbreak was associated with eating Ceasar salad which is made with romaine lettuce. These isolates also shared an unusual inability to metabolize lysine. Traceback of the lettuce revealed that the lettuce in both outbreaks originated from the same producer.