Background:Large national databases have been increasingly used in recent years to determine the rate of adverse events and identify factors associated with altered surgical outcomes. This can be especially useful to evaluate rare events such as 30-day mortality. Despite differences between national pediatric databases, there have been no comparison studies in the pediatric orthopaedic population.Methods:The Healthcare Cost and Utilization Project's Kids' Inpatient Database (KID) along with the American College of Surgeons National Surgical Quality Improvement Program Pediatric (NSQIP Pediatric) databases were queried to identify common pediatric orthopaedic procedures for humeral fractures, scoliosis, slipped capital femoral epiphysis, and femoral fractures during a single year. Clinical characteristics and complications in the 2 databases were compared using Student t test, χ2, or Fisher' exact test.Results:In total, 26,978 patients in the KID and 5186 patients in the NSQIP Pediatric databases were identified. Large differences were observed between the databases in identical procedure categories with respect to age, race, sex, and length of stay. Regardless of procedure, NSQIP Pediatric had statistically higher reported rates of cumulative complications. Surgical site infections and sepsis were consistently observed to be at least twice as common in the NSQIP Pediatric database in comparison to the KID. Overall, complication rates ranged from <1% in humeral fractures to >100% in neuromuscular scoliosis.Conclusions:Clinically and statistically significant differences exist between the KID and NSQIP Pediatric databases. Clinicians and researchers who utilize large databases must understand the differences in data import, quality control, and population sampling in order to provide adequate representation of the population as a whole.Level of Evidence:Level III, prognostic study.