An outbreak of E. coli O157:H7 infections occurred among attendees of a dance camp held between July 11-14 on the campus of Eastern Washington University. The camp was for middle and high school girls. Attendees were from Washington, Montana, and Minnesota. Some of the ill girls attended a church camp in Spokane at the conclusion of the dance camp. Secondary cases were subsequently reported at the church camp and also in the girls' home communities. The cases shared a Pulsed Field Gel Electrophoresis (PFGE), genetic fingerprint, pattern. Case-control study results strongly showed that the Caesar salad, made with Romaine lettuce and served during the July 11 dinner meal and the July 12 lunch, was associated with illness.