To clarify the relationships between intrapartum chorioamnionitis and abnormalities of uterine function, including labor abnormalities, cesarean delivery, and hemorrhage during parturition.We did a retrospective cohort study on 16,226 deliveries between 1986 and 1996 that were identified from the University of California, San Francisco Perinatal Database. Variables included maternal age, parity, birth weight, gestational age, epidural usage, oxytocin usage, cesarean delivery, labor abnormalities, length of labor stages, estimated blood loss, and chorioamnionitis status. Analyses included chi(2), Student t test, and logistic regression.In the chorioamnionitis group, there was a statistically significantly higher proportion of women with labor abnormalities (relative risks [RRs] 2.6-4.1), cesarean delivery (RR 3.3; 95% confidence interval [CI] 3.0, 3.5), hemorrhage after cesarean (RR 1.2; 95% CI 1.1, 1.3), and hemorrhage after vaginal delivery (RR 2.1; 95% CI 1.9, 2.4) compared with the nonchorioamnionitis group. Those findings stayed significant after multivariate analysis for various labor abnormalities (adjusted odds ratios [ORs] ranged 1.3-2.1), cesarean delivery (adjusted OR 1.8; 95% CI 1.5, 2.1), hemorrhage after cesarean (adjusted OR 1.5; 95% CI 1.2, 1.8), and hemorrhage after vaginal delivery (adjusted OR 1.8; 95% CI 1.5, 2.1).Adverse associations between chorioamnionitis and labor abnormalities, cesarean rate, and hemorrhage during parturition appear to be significant, suggesting a deleterious effect of chorioamnionitis on uterine function.