Campers and counselors at a Virginia-based, summer camp developed bloody diarrhea that was found to be caused by E. coli O157:H7. Consumption of rare ground beef during the camp session was assocated with a substantially increased risk for illness. Thirteen ill persons had eaten rare ground beef that had been cooked over a campfire on an overnight trip. Rare ground beef was reported to have been eaten at seven different meals cooked over a campfire. Cultures of some of the available ground beef were performed, but failed to show the presence of E. coli O157:H7.