Objective: This is the first database study to assess the effectiveness of prophylactic preoperative antibiotics (PPAs) in mandible fracture repair., Study Design: Retrospective cohort., Setting: Database study using US inpatient and outpatient insurance claims submitted from July 2006 to March 2015., Methods: The IBM MarketScan Commercial Database was queried for adults aged 18 to 64 years who had undergone first-time mandible fracture repair according to Current Procedural Terminology codes for open and closed repair. Primary outcomes included surgical revision, local infection, and osteomyelitis. Rates were compared between cohorts based on whether or not patients had filled antibiotic prescriptions during the preoperative period alone. The effects of drug abuse and type of mandible repair (open vs closed) were explored. Multivariate Poisson regression models were used to calculate adjusted relative risk estimates, and 95% CIs were used to determine statistically significant differences., Results: A total of 2676 patients were included, with 847 (31.7%) filling PPAs and 1829 (68.3%) filling no antibiotics. Rates were 38.9% for revision, 5.8% for local infection, and 2.1% for osteomyelitis. After multivariate analysis, exposure to PPAs was not associated with surgical revision (adjusted relative risk, 1.04; 95% CI, 0.94-1.15), local infection (1.16; 0.82-1.64), or osteomyelitis (1.21; 0.68-2.14). Patients were more likely to fill PPAs if they underwent open repair (35.3%) versus closed (26.6%) (proportion difference, 8.7%; 95% CI, 5.2%-12.2%), but exposure to antibiotics did not predict outcomes on subgroup analysis., Conclusion: PPAs do not improve mandible repair outcomes, regardless of repair type.