In May 2000 a scout camp was held on an agricultural showground in New Deer, Aberdeenshire. There were 337 campers at the event, comprising 233 cubs, scouts, and venture scouts, and 104 adults. The event was abandoned early because of heavy rainfall. Twenty campers who became ill between 28 May and 3 June were confirmed as having E. coli O157 infection. Preliminary investigation did not suggest a food vehicle but did indicate environmental exposure at the camp as a risk factor. Subsequent investigations supported the hypothesis that transmission of E. coli O157 was from the environment to cases by contaminated hands, either directly from hand to mouth, or via food. As a result of the investigation the Aberdeenshire Council and the Scout Association jointly prepared interim guidelines to reduce the risk of E. coli O157 infection at scout camps.