Histologic results of the placenta are usually not available within the first days of life. We identified inflammatory variables in tracheal aspirates and blood that were associated with histologic chorioamnionitis (HC). A derivation cohort consisted of 62 neonates and a validation cohort of 57 neonates with a gestational age < 31 wk and ventilated on d 1. Tracheal aspirates were taken on d 1 and on d 3, if the patient was still ventilated. HC was diagnosed by light microscopy. Logistic regression was used to identify independent factors in the derivation cohort associated with HC at d 1, 2, and 3. Model performance was studied using receiver operating characteristic curve analysis. Independent factors associated with HC were, at d 1, tracheal aspirate IL-8 >or= 917 pg/mL (odds ratio, 60.7; 95% confidence interval, 11-328); at d 2, blood C-reactive protein >or= 14 mg/L (odds ratio, 9.2; 95% confidence interval, 2-38), blood white blood cell count >or= 10400/mm3 (odds ratio, 7.4; 95% confidence interval, 2-28); and at d 3, blood neutrophil count >or= 4968/mm3 (odds ratio, 14; 95% confidence interval, 3-57). The association with HC was less at d 3 (area under receiver operating characteristic curve, 0.77) when compared with the d 1 model (area under the curve, 0.88; p = 0.09). The models performed equally well in the validation cohort (goodness-of-fit test, p > 0.05). We conclude that the d 1 and d 2 models can be used as diagnostic factors for HC. Tracheal aspirate IL-8 taken immediately after birth was equally accurate in the diagnosis of HC as systemic inflammatory response at d 2 and better than on d 3.