In the United States, Norwalk-like viruses (NLVs) cause an estimated 23 million episodes of illness, 50,000 hospitalizations, and 300 deaths each year. NLVs can be transmitted by fecally contaminated food and water and by direct person-to-person contact or through droplets of infected persons. Outbreaks of NLV-associated gastrointestinal illness are common in military settings. During May 13-19, 2002, a total of 29 British soldiers and staff of a field hospital in Afghanistan became acutely ill after a short incubation period with vomiting, diarrhea, and fever. This report summarizes the investigation of this outbreak and underscores the importance of the diagnostic capacity for NLVs.