BACKGROUND: Many antibiotics are prescribed inappropriately in pediatric emergency departments (PEDs), but little data are available in these settings about effective interventions based on guidelines that follow the antimicrobial stewardship principle. Our aim was to assess the impact of implementing the 2011 national guidelines on antibiotic prescriptions for acute respiratory tract infection (ARTI) in PEDs. METHOD: We conducted a multicentric, quasiexperimental, interrupted time series analysis of prospectively collected electronic data from 7 French PEDs. We included all pediatric patients who visited a participating PED during the study period from November 2009 to October 2014 and were diagnosed with an ARTI. The intervention consisted of local protocol implementation, education sessions, and feedback. The main outcome was the antibiotic prescription rate of discharge prescriptions for ARTI per 1000 PED visits before and after implementation, analyzed using the segmented regression model. RESULTS: We included 242534 patients with an ARTI. The intervention was associated with a significant change in slope for the antibiotic prescription rate per 1000 PED visits (-0.4% per 15-day period, P = .04), and the cumulative effect at the end of the study was estimated to be -30.9%, (95% CI [-45.2 to -20.1]), representing 13136 avoided antibiotic prescriptions. The broad-spectrum antibiotic prescription relative percentage decreased dramatically (-62.7%, 95% CI [-92.8; -32.7]) and was replaced by amoxicillin. CONCLUSION: Implementation of the 2011 national French guidelines led to a significant decrease in the antibiotic prescription rate for ARTI and a dramatic drop in broad-spectrum antibiotic prescriptions, in favor of amoxicillin.