Objectives. To describe the epidemiology of nosocomial infections in pediatric intensive care units (ICUs) in the United States. Background. Patient and ICU characteristics in pediatric ICUs suggest the pattern of nosocomial infections experienced may differ from that seen in adult ICUs. Methods. Data were collected between January 1992 and December 1997 from 61 pediatric ICUs in the United States using the standard surveillance protocols and nosocomial infection site definitions of the National Nosocomial Infections Surveillance System’s ICU surveillance component. Results. Data on 110 709 patients with 6290 nosocomial infections were analyzed. Primary bloodstream infections (28%), pneumonia (21%), and urinary tract infections (15%) were most frequent and were almost always associated with use of an invasive device. Primary bloodstream infections and surgical site infections were reported more frequently in infants aged 2 months or less as compared with older children. Urinary tract infections were reported more frequently in children >5 years old compared with younger children. Coagulase-negative staphylococci (38%) were the most common bloodstream isolates, and aerobic Gram-negative bacilli were reported in 25% of primary bloodstream infections. Pseudomonas aeruginosa (22%) was the most common species reported from pneumonia and Escherichia coli (19%), from urinary tract infections. Enterobacter spp. were isolated with increasing frequency from pneumonia and were the most common Gram-negative isolates from bloodstream infections. Device-associated infection rates for bloodstream infections, pneumonia, and urinary tract infections did not correlate with length of stay, the number of hospital beds, or season. Conclusions. In pediatric ICUs, bloodstream infections were the most common nosocomial infection. The distribution of infection sites and pathogens differed with age and from that reported from adult ICUs. Deviceassociated infection rates were the best rates currently available for comparisons between units, because they were not associated with length of stay, the number of beds in the hospital, or season. Pediatrics 1999;103(4). URL: http://www.pediatrics.org/cgi/content/full/103/4/ e39; intensive care units, pediatrics, epidemiology, cross infection, risk factors, bacteremia, pneumonia, urinary tract infections. ABBREVIATIONS. PICU, pediatric intensive care unit; ICU, intensive care unit; NNIS, National Nosocomial Infection Surveillance; UTI, urinary tract infection. Pediatric intensive care units (PICUs) differ from adult intensive care units (ICUs) in a number of ways, apart from the age of their patients. First, they are usually multidisciplinary, because there are too few patients to justify separate medical and surgical units.1 Second, they frequently lack the physical barriers between patients now commonly present in adult ICUs. Third, fewer children than adults in ICUs have chronic or degenerative organ system disorders2 and probably the majority of children in PICUs will, if successfully treated, return to a normal productive life. Nosocomial infections represent an important cause of morbidity and mortality in this population.3 The overall mortality attributable to pediatric nosocomial infections has been estimated at 11%.4 This report describes the epidemiology of nosocomial infections in children within PICUs in the United States that use the standard surveillance protocols and nosocomial infection site definitions from the National Nosocomial Infections Surveillance (NNIS) System of the Centers for Disease Control and Prevention.