Antibiotic-resistant Gram-negative bacilli are a prominent and growing problem among hospitalized children. Epidemics caused by these organisms have been implicated in many outbreaks in children's hospitals, primarily in neonatal intensive care units. These epidemics are characterized by efficient patient-to-patient transmission of the outbreak clone via the hands of caregivers and through exposure of contaminated inanimate sources. The epidemiology of these resistant organisms in pediatric hospitals during endemic periods is more complex. The isolates cultured from hospitalized individuals in the absence of an outbreak usually are unique to each individual and are derived from the patient's endogenous flora or other disparate sources. As in adults, chronic care facilities for children represent significant reservoirs of antibiotic-resistant bacilli that are circulated back into the acute care hospital environment when the child becomes ill.