Emergency department triage systems are designed to prioritize patients based on the level of illness. Inappropriate triage can lead to delays in care and adverse events. In Europe, the Manchester Triage System is a widely used algorithm that classifies patients based on five levels of urgency with a corresponding maximum waiting time. This study sought to assess the effectiveness of the Manchester Triage System in children requiring admission to the intensive care unit (ICU). Analyzing more than 50,000 consecutive emergency department visits of children younger than 16, the authors determined that almost one third of children admitted to the ICU were undertriaged. Risk factors identified for undertriage included age younger than 3 months, type of medical presenting problem, presence of underlying chronic conditions, referral by a specialist or emergency medical services, and arrival during the evening or at night. These findings suggest that the Manchester Triage System inappropriately triages a significant proportion of children requiring ICU admission and that modifications should be made to improve safety in pediatric emergency care. A previous WebM&M commentary discussed the challenges of triage in the emergency department.