To describe the structure and organization of pediatric intensive care units (ICUs) in the United States. We directed a mail survey to pediatric ICU medical and nursing directors and hospital quality assurance officers. A total of 201 of 301 hospitals with pediatric ICUs initially responded. Telephone confirmation of the mail survey (n = 193) and telephone data collection for mail survey nonresponders (n = 42) were also undertaken. The largest proportion (40.0%) of pediatric ICUs had four to six beds per unit, while only 6.0% had > 18 beds per unit. The admissions per year averaged 528 +/- 24, and the mortality rates averaged 5.5 +/- 0.2%. Only 79.6% of the pediatric ICUs had full-time medical directors. A pediatric intensivist was available to 73.2% of the units. Physician coverage for 24 hrs/day dedicated only to the pediatric ICU was present in 48.5% of hospitals. As ICU size increased, the estimated mortality rates increased, as did the percentages with full-time directors, pediatric intensivists, and 24 hrs/day dedicated coverage. Medical school affiliation existed for 79.6% of pediatric ICU hospitals, and 81.1% of these hospitals were the primary teaching program sites for pediatrics. Other ICUs caring for children were present in 30.2% of the hospitals. The mail survey respondents were stratified using four factors: size, teaching status, intensivist status, and coordination of care status. A total of 16 respondents were randomly selected for an ongoing outcomes study of the importance of these factors. Substantial diversity exists in pediatric ICU structure and organization. Determining factors associated with quality of care is important for improving outcomes.