BACKGROUND: The Core Elements of Outpatient Antibiotic Stewardship provide a framework to improve antibiotic use. We report the impact of core elements implementation within Veterans Health Administration sites. METHODS: In this quasiexperimental controlled study, effects of an intervention targeting antibiotic prescription for uncomplicated acute respiratory tract infections (ARIs) were assessed. Outcomes included per-visit antibiotic prescribing, treatment appropriateness, ARI revisits, hospitalization, and ARI diagnostic changes over a 3-year pre-implementation period and 1-year post-implementation period. Logistic regression adjusted for covariates (odds ratio [OR], 95% confidence interval [CI]) and a difference-in-differences analysis compared outcomes between intervention and control sites. RESULTS: From 2014-2019, there were 16 712 and 51 275 patient visits within 10 intervention and 40 control sites, respectively. Antibiotic prescribing rates pre- and post-implementation within intervention sites were 59.7% and 41.5%, compared to 73.5% and 67.2% within control sites, respectively (difference-in-differences, P < .001). Intervention site pre- and post-implementation OR to receive appropriate therapy increased (OR, 1.67; 95% CI, 1.31-2.14), which remained unchanged within control sites (OR,1.04; 95% CI, .91-1.19). ARI-related return visits post-implementation (-1.3% vs -2.0%; difference-in-differences P = .76) were not different, but all-cause hospitalization was lower within intervention sites (-0.5% vs -0.2%; difference-in-differences P = .02). The OR to diagnose non-specific ARI compared with non-ARI diagnoses increased post-implementation forintervention (OR, 1.27; 95% CI, 1.21 -1.34) but not control (OR, 0.97; 95% CI, .94-1.01) sites. CONCLUSIONS: Implementation of the core elements was associated with reduced antibiotic prescribing for RIs and a reduction in hospitalizations. Diagnostic coding changes were observed.