Although right main bronchus intubation is associated with adverse consequences, the optimal endotracheal tube (ETT) tip position above the carina in neonates is not known. The aim of this study was to determine the association between ETT tip position and adverse pulmonary effects as assessed by chest radiographs (CXRs). Lung aeration was examined after masking ETT positions in the first two CXRs taken after birth in 74 consecutive ventilated premature infants <or= 28 weeks. All the CXRs of the infants during the first week were examined for predefined combined adverse pulmonary outcomes by two examiners (right upper lobe collapse, localized pulmonary interstitial emphysema [PIE], and pneumothorax). Infants who had ETT tips below T4 or in the right main bronchus were excluded. The ETT tip was above T1 in 4 (5.4%), at T1 in 11 (14.8%), at T2 in 19 (25.6%), at T3 in 27 (36.5%), and at T4 in 13 (17.6%) infants. The patients were categorized into group A (ETT tips at T1/2) or group B (ETT above T1 or below T2). The combined adverse pulmonary outcome of pneumothorax, localized PIE, and right upper lobe collapse was significantly higher in group B compared with group A ( P=0.03). On logistic regression analysis, the only independent association for adverse pulmonary outcome and asymmetrical lung aeration was the ETT position. The odds ratio for developing nonuniform lung aeration was 6 (95% confidence interval [CI] 1.8, 20) and for adverse pulmonary outcome was 8 (95% CI 1.1, 73) when the ETT tip was at T3/T4 compared with T1/2. We concluded that the ETT tip should be kept at the level of the first or second thoracic vertebrae in extremely premature babies to reduce the incidence of nonuniform lung aeration and adverse pulmonary outcomes.