We conducted a prospective study in three hospitals in Lima in human immunodeficiency virus (HIV) children to determine the frequency of diarrheagenic Escherichia coli. Five E. coli colonies/patients were studied by a multiplex real-time polymerase chain reaction to identify the six currently recognized groups of diarrhea-associated E. coli. We have analyzed 70 HIV-associated diarrheal and 70 control samples from HIV-infected children without diarrhea. Among the diarrheal episodes 19% were persistent, 3% dysenteric, and 33% were associated with moderate or severe dehydration. The diarrheagenic E. coli were the most commonly isolated pathogens in diarrhea (19%) and control samples (26%) (P = 0.42), including enteroaggregative (6% versus 10%), enteropathogenic (6% versus 10%), and enterotoxigenic E. coli (4% versus 3%), respectively. The HIV-infected children with diarrhea had the worse age-related immunosuppression, higher viral loads, and were on highly active antiretroviral treatment (HAART) less often than HIV-infected children without diarrhea. Diarrheagenic E. coli were highly resistant to ampicillin (74%) and cotrimoxazole (70%). Copyright © 2010 by The American Society of Tropical Medicine and Hygiene.