We report an outbreak of norovirus(NoV) which occurred at a military training center in Peru. Thirteenstool samples that were taken from initial cases turned out positive for NoV GII by RT-PCR. A case-control study was performedto determine factorsassociated with infection.164 probable cases (45.2%clinical attack rate) were identified. The only factor associatedwith infection was "having shared room with a case" (ORa = 1.7; 95% CI 1.1 to 2.7).Epidemiological findings suggestthat the virus was spread person to person. Future investigations of outbreaks of diarrhea in Peru should consider the NoV as an etiologicagent.