The hospitalization of a child is one of the most traumatic episodes of parenthood. The fear, frustration, anger, and loss of control can be overwhelming to the parents of the critically ill child. Acute care hospitalizations such as those that occur in the neonatal intensive care units (NICUs) and pediatric intensive care units (PICUs) are especially distressing to every member of the family. Unfortunately, families subjected to both NICU and PICU admissions experience two distinctive cultures with very different philosophies and goals. In spite of the best intentions of health care providers, the obvious cultural differences between the NICU and PICU potentially aggravate the stress suffered by families. Unfortunately, most NICU and PICU staff members are unfamiliar with the contrasting cultures. The mean localization index for pediatric discharges was 20 percentage points lower than for Medicare cases, indicating a poorer fit of the traditional geographic system for children. The volume of pediatric cases did not appear to be associated with the magnitude of index divergence between the two age groups. Pediatric medical and surgical case subgroups gave very similar results, and both groups differed substantially from seniors. Location of children's hospitals and local pediatric bed supply were associated with Medicare-pediatric divergence. There was little visual correspondence between the maps of traditional and pediatric-specific HSAs. Studies of regional variation in child health care have identified differences in the supply of medical care resources and in the use of these resources in relation to population need. Although small area analysis is the most widely used method for studying regional variation in child health services, relatively few pediatric studies have been published in contrast to an extensive adult literature. Small area analysis first defines local medical service area borders that best reflect patients' utilization patterns. These areas are then used to study geographic variation in health care resources, such as the per ca pita supply of physicians or hospital beds, and variation in utilization levels, such as hospital discharge rates. Although termed small area analysis, the geographic areas reflect the scale of the medical care under study – small for primary care, medium for common hospital admissions, or large for tertiary care (e.g. neonatal intensive care). What is common in small area analysis is that patients are linked to providers and systems of health care through the utilization-based definition of health care market areas. Therefore the health care system serving children may well have different geographic attributes than the one serving the elderly. Validation of Dartmouth HSAs for children would bring an important new tool to the efforts to improve the delivery of care to children. If these areas are not appropriate for use in pediatric health services research, then child-specific areas should be defined. The HSA variable of interest was index of localization, which is the percentage of patients residing in an HSA that were hospitalized in that HSA. Thus, 100% is perfect localization or 'fit'. Four localization indices were computed for each HSA: one for Medicare Part A discharges (primarily seniors), one for all pediatric discharges, one for pediatric medical DRGs, and one for pediatric surgical DRGs. The reason for dividing pediatric cases into medical and surgical groups was to see if the degree of specialization of care might be a factor in the divergence of pediatric and Medicare geography. Pediatric medical cases (e.g. asthma) usually require less specialization for treatment than surgical cases. It appears that greater local commitment to inpatient children's services tends to keep children in their "home" area. However, it should be noted that, while "number of pediatric beds", an American Hospital Association survey variable, may roughly represents an institution's commitment to children, the variable is not without problems. For example, the AHA questionnaire instructions do not set an age limit for "pediatric". Furthermore, although the questionnaire instructions clearly state that only beds reserved for children should be counted, some respondents might count as pediatric those swing beds that are "for" children but filled by adults as the need arises. Others might not count these flexible beds as pediatric beds. Still, we think it is a useful variable and it performs as expected in our analyzes safety and efficacy of intraosseous needle placement among health care provider groups in the setting of pediatric critical care transport.. Children undergoing pediatric critical care transport between January 1, 2000, and March 31, 2002, requiring intraosseous access before arrival to the pediatric intensive care unit. During the study period, the transport team performed 1,792 transports and identified 47 patients requiring 58 intraosseous placements. These were placed by emergency medical technician paramedics (18%), referring emergency medicine physicians (42%), and the transport team members (40%). The intraosseous needles were placed with a mean of 1.2 attempts per placement and a first attempt success rate of 78%. Main site of placement was the proximal anterior tibia (95%). Access was maintained for a mean of 5.2 hrs. The intraosseous needle was used for fluids, medications, and laboratory studies. Admitting diagnoses included respiratory distress (28%), cardiopulmonary arrest (26%), neurologic insults (17%), dehydration (15%), sepsis (11%), and other (3%). Ages ranged from 3 wks to 14 yrs (mean 2.2 yrs) and weights from 2.1 to 60 kg (mean 12.3 kg). Complications were noted in seven of 58 (12%), all limited to local edema or infiltration. Intraosseous placement is frequently needed in the care of critically ill pediatric patients before they reach the pediatric intensive care unit. We have demonstrated that intraosseous needles can be placed safely with similar rates of success when comparing different provider groups. Emergency medical technician-paramedics, emergency medicine physicians, and pediatric critical care transport teams should be familiar with intraosseous placement.