During the recent cholera epidemic which affected Peru and other Latin American countries, fresh stool samples of 100 hospitalized children were assessed February through April 1991. The children had been admitted because of profuse watery diarrhea. The microbiologic study of wet mount preparations showed curved bacteria suspicious for cholera agent and confirmed afterward to be Vibrio cholerae 01 serotype Inaba. In 30% of such cases, besides the curved bacteria, a strikingly large number of trophozoites of Giardia intestinalis were observed. The same samples studied by permanent stains confirmed the presence of Giardia trophozoites. To our knowledge, the association of Giardia with serious epidemic cholera infection has not been previously described. All patients were admitted because of severe dehydration requiring intravenous fluid replacement, which might suggest a synergistic role for the above-noted coinfection. Adequately designed case-control studies are needed to ascertain the frequency and the pathophysiologic and clinical significance of such an unusual association. © 1995, Wilderness Medical Society. All rights reserved.