OBJECTIVE: To evaluate the association of institutional protocols for vaginal preparation with antiseptic solution and the surgical site infection rate in women undergoing cesarean delivery during labor. METHODS: This is a secondary analysis of a multicenter randomized controlled trial of adjunctive azithromycin prophylaxis for cesarean delivery performed in laboring patients with viable pregnancies. The primary outcome for this analysis was the rate of superficial or deep surgical site infection within 6 weeks postpartum, as per Centers for Disease Control and Prevention criteria. Maternal secondary outcomes included a composite of endometritis, wound infection or other infections, postoperative maternal fever, length of hospital stay, and the rates of hospital readmission, unexpected office visits, and emergency department visits. RESULTS: A total of 523 women delivered in institutions with vaginal antisepsis policies before cesarean delivery and 1,490 delivered in institutions without such policies. There was no difference in superficial and deep surgical site infection rates between women with and without vaginal preparation (5.5% vs 4.1%; odds ratio [OR] 1.38, 95% CI 0.87-2.17), even after adjusting for possible confounders (adjusted OR 0.86, 95% CI 0.43-1.73). The lack of significant benefit was noted in all other maternal secondary outcomes. CONCLUSION: Institutional policies for vaginal preparation before cesarean delivery were not associated with lower rates of surgical site infection in women undergoing cesarean delivery during labor. (Obstet Gynecol 2018;132:371-6).