OBJECTIVE: To test the hypothesis that pediatric residents would have shorter time to attempted defibrillation using automated external defibrillators (AEDs) compared with manual defibrillators (MDs). STUDY DESIGN: A prospective, randomized, controlled trial of AEDs versus MDs was performed. Pediatric residents responded to a simulated in-hospital ventricular fibrillation cardiac arrest and were randomized to using either an AED or MD. The primary end point was time to attempted defibrillation. RESULTS: Sixty residents, 21 (35%) interns, were randomized to 2 groups (AED = 30, MD = 30). Residents randomized to the AED group had a significantly shorter time to attempted defibrillation [median, 60 seconds (interquartile range, 53 to 71 seconds)] compared with those randomized to the MD group [median, 103 seconds (interquartile range, 68 to 288 seconds)] (P < .001). All residents in the AED group attempted defibrillation at <5 minutes compared with 23 (77%) in the MD group (P = .01). CONCLUSIONS: AEDs improve the time to attempted defibrillation by pediatric residents in simulated cardiac arrests. Further studies are needed to help determine the role of AEDs in pediatric in-hospital cardiac arrests.