Objectives: To determine whether intrapartum chlorhexidine vaginal irrigation reduces microbial colonization of the chorioamnion or placenta. Methods: Secondary analysis was made of a randomized trial. Cultures for aerobic and anaerobic bacteria, Mycoplasma species and Ureaplasma urealyticum were performed using standard isolation techniques. Results: The placentas of 83 trial participants allocated to chlorhexidine and 93 allocated to placebo underwent evaluation. These two groups were statistically balanced for risk factors for infection. Aerobic bacteria were isolated from 47% of the chlorhexidine placentas vs. 51% of the placebo placentas (relative risk 0.9, 95% confidence interval 0.7-1.3), anaerobic bacteria from 30% and 35%, respectively (0.8, 0.5-1.3), group B streptococcus from 12% and 15% (0.8, 0.4-1.7), U. urealyticum from 18% and 29% (0.6, 0.4-1.1), Mycoplasma species from 6% and 11% (0.6, 0.2-1.6), and any organism from 57% and 67%, respectively (0.8, 0.7-1.1). Conclusions: Intrapartum chlorhexidine vaginal irrigation was associated with non-significant reductions in the rates of placental microbial isolation. © 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.