An outbreak of E. coli O157:H7 infections occurred following an October 6, 2001 pancake breakfast that was held at the University of Wisconsin's Stock Pavilion. The pavilion was used for many activities including livestock classes. Environmental samples and fecal samples from humans and cattle were collected. A long wait for breakfast was associated with risk of illness. E. coli O157:H7 was isolated from cattle and from sawdust on the pavilion floor that matched the E. coli O157:H7 strain that had been isolated from the people. Although cow manure had been observed on the pavilion floor, the cows were not present during the breakfast event.