PURPOSE:Infections can lead to flap failure, increased mortality, postoperative complications, and increased length of hospitalization. This study explores the association between Abscess formation within 30 days of microsurgical free tissue transfer surgery to the head and neck and the perioperative antibiotic prophylactic regimen. METHODS: This retrospective cohort study included all patients who underwent head and neck reconstruction with free tissue transfer from January 2012 through August 2023. Patients received antibiotic prophylaxis perioperative with one of the following regimens: Ampicillin/Sulbactam (AMP), Cefazolin with metronidazole (CZ-MTZ), Clindamycin, or Levofloxacin with Metronidazole (LEV-MTZ). Patients with other antibiotics prophylaxis were excluded. The main study outcome was a neck infection requiring returning to the operating room for washing out. Statistical analysis was performed using univariate and multivariate regression analysis. RESULTS:970 patients were included. The rate of infection was (n=44, 4.5%). The distribution of comorbidities measured by Charlson Comorbidity Index in those who developed infection was similar to those who did not (p=0.655). In univariate analysis, AMP, CZ-MTZ, and LEV-MTZ were significantly less associated with infection compared to clindamycin (OR 0.205 95%CI: 0.100-0.418), (OR 0.057, 95%CI: 0.022-0.146) (OR 0.115, 95%CI: 0.014-0.910) respectively. However, the statistical significance after controlling for diabetes and prior radiation therapy persisted only for AMP and CZ-MTZ (OR 0.217, 95%CI: 0.106-0.445), (OR 0.065, 95%CI: 0.256-0.165). CONCLUSIONS:CZ-MTZ is associated with a decreased postoperative infection rate compared to AMP and Clindamycin, even after controlling for patient factors.