BACKGROUND Elevated cytokine concentrations were observed in tracheal aspirate fluid (TAF) of infants on mechanical ventilation who subsequently developed bronchopulmonary dysplasia (BPD). However, there are few reports that systematically evaluate the amount of TAF as an indicator of BPD development. OBJECTIVE To clarify whether TAF volume during the first week of life predicts BPD development in extremely low gestational age newborns (ELGANs). METHODS We analyzed 51 infants, born at gestational age of <28 weeks and ventilated for more than 7 days after birth, among whom, 26 were diagnosed with BPD based on the clinical definition of oxygen dependence at 36 weeks postmenstrual age (BPD group) and 25 were included in the non-BPD group. Sum of TAF scores (STS) was calculated by semi-quantification of TAF volume at each suctioning and the suctioning frequency during the first week of life. RESULTS STS was significantly higher in the BPD group than in the non-BPD group (median (interquartile range): 77 (29-126) vs. 28 (22-59), p<0.001). STS (cut-off, 60) with area under the curve in receiver operating analysis of 0.75 was significantly predictive of BPD development. Multivariate logistic regression analysis adjusted for perinatal characteristics showed that STS≥60 was a significant risk factor for BPD development (odds ratio, 7.50; confidence interval, 1.16-48.40, p=0.034). CONCLUSIONS Increased TAF volume during the first week of life was an independent predictor for BPD development in ventilated ELGANs, indicating that increased pulmonary capillary permeability may influence the pathogenesis of BPD.