A cluster of E. coli O157:H7 cases, including some who developed hemolytic uremic syndrome (HUS), were reported among children who had visited a petting zoo at the North Carolina State Fair. Further investigation found additional related illnesses. The fair had two petting zoos. A case control study was performed. No specific food, beverage, or recreational water exposure was associated with illness. Visiting petting zoo B was associated with a significantly increased risk of illness. Petting zoo B had sanitation problems. This petting zoo allowed extensive contact with goats and sheep and their bedding in a crowded circumstance. Visits to petting zoo A were not associated with illness.