In July 2011, the U.S. Air Force School of Aerospace Medicine (USAFSAM) Epidemiology Consult Service investigated an ongoing outbreak of acute gastrointestinal (GI) illness--characterized by vomiting, nausea, diarrhea, and stomach cramps--that affected cadets and support personnel at a field training location at the U.S. Air Force Academy. Six outbreak-related stool specimens were confirmed by RT-PCR to be infected with norovirus, genogroup I. Overall, 290 cases (suspected and confirmed) of norovirus-related GI illness were recorded; the estimated attack rate among 1,359 cadets was 18%. The investigation suggested that norovirus was introduced into the field dining facility by one or more food service workers, possibly transmitted via common use serving utensils, and then further spread among cadets by person-to-person contact. Numbers of new cases sharply declined after ill cadets were segregated in separate tents for convalescence, and after all cadets moved from field billets (i.e., tents) to dormitories after completing the field training.