OBJECTIVE: To investigate the association of chorioamnionitis, and secondarily its duration, on neonatal adverse outcomes for infants born <34 weeks vs. ≥34 weeks. STUDY DESIGN: A secondary analysis from the observational U.S. Consortium on Safe Labor Study. The exposure was chorioamnionitis, and secondarily, its estimated duration. The composite outcome included pneumonia, seizure, necrotizing enterocolitis, sepsis, periventricular/intraventricular/cerebral hemorrhage, mechanical ventilation, and neonatal death. Multivariable logistic regression with generalized estimating equations was used, stratified by gestational age at delivery. RESULTS: Among 221,274 deliveries, the odds of the neonatal adverse outcome <34 weeks was 2-fold higher among infants exposed to chorioamnionitis vs. those who were not (62.0 vs. 47.7%; AOR: 1.86; 95%CI: 1.25-2.75), and was ~3.5-fold higher ≥34 weeks (9.2 vs. 2.5%; AOR: 3.34; 95% CI: 2.35-4.76). The estimated duration of chorioamnionitis did not change the above associations. CONCLUSIONS: Chorioamnionitis was associated with an approximately 2- and 3.5-fold increased odds of neonatal adverse outcomes <34 and ≥34 weeks, respectively, regardless of its estimated duration.