Objective. To determine the incidence of Vibrio cholerae O1-associated diarrhea in children during the onset of the 1991 cholera epidemic in Peru. Methods. Stool cultures were obtained from children (mean age, 26 months) participating in a prospective community-based study of diarrhea in a periurban community in Lima between February and May, 1991. Results. Of the 409 diarrheal episodes cultured V. cholerae O1 was isolated in 14 (3.4%) episodes. This represented an incidence of 0.11 episode per child year, higher than previously reported rates in children from endemic cholera areas. Most cases were mild; only 1 case required hospitalization. Conclusions. Our study indicates that from the beginning of this epidemic, V. cholerae O1 caused diarrhea in children as well as adults and should therefore be considered as one of the possible pathogens when children from a cholera- affected area develop diarrhea.