• A prospective study of the epidemiology of nosocomial infections was undertaken in a large pediatric hospital. Infections were identified during a 12-month period with the use of medical record audits, indices identifying high-risk patients, and analysis of positive cultures and rapid diagnostic tests for viruses, fungi, and bacteria. The attack rate of the entire hospital population surveyed was 4.1 nosocomial infections per 100 patients discharged. In contrast with studies of patients in general hospitals that included comparatively few children, the most common sites of nosocomial infections were the respiratory and gastrointestinal tracts. Staphylococcus aureus was the most commonly isolated pathogen. However, rotavirus was identified more frequently than Escherichia coli, and documented viral infections were more common than infections caused by gram-negative bacilli.