In late January 1991, epidemic cholera appeared in Peru. Within 2 months, 7922 cases and 17 deaths occurred in Piura, a Peruvian city of 361,868. A hospital-based culture survey showed that 79°/o-86°/o of diarrhea cases were cholera. High vibriocidal antibody titers were detected in 34% of the asymptomatic population. A study of 50 case-patients and 100 matched controls demonstrated that cholera was associated with drinking unboiled water (odds ratio [OR], 3.9; 95% confidence interval [CI], 1.7-8.9), drinking beverages from street vendors (OR, 14.6; CI, 4.2- 51.2), and eating food from street vendors (OR, 24.0; CI, 3.0-191). In a second study, patients were more likely than controls to consume beverages with ice (OR, 4.0; CI, 1.1-18.3). Ice was produced from municipal water. Municipal water samples revealed no or insufficient chlorination, and fecal coliform bacteria were detected in samples from 6 of 10 wells tested. With epidemic cholera spreading throughout Latin America, these findings emphasize the importance of safe municipal drinking water. © 1992 the University of Chicago.