OBJECTIVE: To determine the incidence of physiologic deterioration in critically ill and injured pediatric patients during interhospital transport with air and ground ambulance DESIGN: Prospective, descriptive study SETTING: All children were treated in regional hospitals and then transported to a pediatric tertiary care center. PATIENTS: Children (n = 100) with a median age of 1.4 years (range 1 week to 18 years) MAIN RESULTS: Three sets of physiologic scores were calculated: at the time of referral, on departure from the referring hospital, and arrival at the tertiary care center. The incidence of significant physiologic deterioration based on the calculated physiologic scores was 5.6% (n = 4) during ground and 3.4% (n = 1) during air ambulance transports. Critical events occurred in 15% of ground and 31% of air ambulance transports. CONCLUSION: No difference existed in the incidence of adverse events or physiologic deterioration when air ambulance transports were compared with ground ambulance transports for critically ill children by our team. The physiologic scoring system we chose is simple and easy to use for quality assurance.