OBJECTIVE To estimate the rate of histologic chorioamnionitis in the presence of diagnosed clinical chorioamnionitis and determine whether clinical markers of maternal and neonatal infection are associated with histologic chorioamnionitis. METHODS We identified singleton pregnancies from 1996 in which discharge diagnoses included clinical chorioamnionitis and reviewed maternal and neonatal records for clinical evidence of chorioamnionitis and suspected or confirmed neonatal infections. Placentas were examined for acute histologic chorioamnionitis. RESULTS One hundred thirty-nine pregnancies with the discharge diagnosis of maternal clinical chorioamnionitis were included. Eighty-six (61.9%) had the clinical diagnosis supported by histologic chorioamnionitis. Histologic chorioamnionitis was associated with an earlier gestational age at delivery (35.7+/-6.5 weeks versus 38.6+/-2.9 weeks, P = .002), lower epidural usage (72.1% versus 92.5%, P = .004), less internal monitoring (47.7% versus 75.5%, P = .001), and possible neonatal sepsis (60.5% versus 35.8%, P = .005). For 19 of 71 (26.8%) infants with possible neonatal sepsis, placentas did not show histologic chorioamnionitis. CONCLUSIONS Clinical chorioamnionitis and possible neonatal infection were not supported by histologic evidence for infection in 38.1% and 26.8% of cases, respectively, suggesting other noninflammatory causes of signs and symptoms.