BACKGROUND We have isolated mesenchymal stem cells (MSCs) from tracheal aspirates of premature infants with respiratory distress. Under the influence of transforming growth factor β, MSCs differentiate into α-smooth-muscle actin-expressing myofibroblasts. Myofibroblasts are increased in the lungs of patients with bronchopulmonary dysplasia (BPD), a chronic lung disease of prematurely born infants. OBJECTIVE We tested whether isolation of MSCs from tracheal aspirates of premature infants with respiratory distress during the first week of life correlates with BPD. METHODS Eighty-four infants born at a gestational age of <33 weeks and requiring mechanical ventilation were studied. Aspirates were collected during suctioning and centrifuged. Cell pellets were resuspended in culture medium and plated. Adherent cells were grown to confluence. RESULTS MSCs were isolated from the tracheal aspirates of 56 infants; 28 aspirate samples showed no MSCs. There was no statistical difference in gestational age or birth weight between the MSC and no-MSC groups. In the MSC group, 12 infants died and 25 developed BPD, as defined by a requirement for supplemental oxygen at 36 weeks' postmenstrual age. In the no-MSC group, 6 infants died and 1 developed BPD. Accounting for potential influences of gender, birth weight, gestational age, number of tracheal aspirate samples taken, and the duration of endotracheal intubation (up to 7 days), isolation of MSCs increased the adjusted odds ratio of BPD more than 21-fold (95% confidence interval: 1.82-265.85). CONCLUSIONS Isolation of tracheal aspirate MSCs predicts the development of BPD, which suggests that MSCs play an important role in the pathogenesis of this disease.