Pediatric inpatients with chronic medical conditions had significantly higher rates of iatrogenic medical errors in this study, which analyzed the AHRQ-sponsored Kids' Inpatient Database. Nearly half of the pediatric inpatients in this large national sample had at least one chronic medical condition, and among these patients, the overall medical error rate was almost four times higher than the rate among children without chronic medical conditions. This association remained statistically significant after adjusting for patient and hospital characteristics, disease severity, and length of stay. The association between medical complexity and the risk of preventable harm while hospitalized has also been demonstrated in adult inpatients.