Objective. The purpose of this study was to assess the incidence and outcome of managing a pneumothorax without tube thoracostomy and to determine the clinical and laboratory characteristics that distinguish infants with a pneumothorax who can be treated without chest-tube insertion. Methods. A retrospective study was performed of neonates who were admitted to the neonatal intensive care unit at the University at Alabama at Birmingham from 1992 to 2005 and had a pneumothorax while on mechanical ventilation. Infant characteristics, respiratory and radiologic diagnoses, and respiratory management data (ventilator settings and blood gases) were compared between infants who initially were treated with a chest tube versus those initially treated without a chest tube. Results. A total of 136 ventilated infants with pneumothorax while on a ventilator were included in the final analysis;101 (74%) were treated initially with a chest tube and 35 (26%) without a chest tube. Of those who did not receive a chest tube initially, 14 were treated with needle aspiration and 21 with expectant treatment. Infants who were treated initially without a chest tube were on a lower ventilator settings (mean airway pressure and fraction of inspired oxygen) and had better blood gases (arterial oxygen saturation, PCO 2, and pH) compared with infants who were treated with a chest tube. Infants who were treated initially with needle aspiration were more likely to require subsequent chest-tube insertion than infants who had expectant treatment (43% vs 10%). Conclusions. It is possible to treat expectantly without initial chest-tube placement a select group of ventilated neonates with pneumothorax. Copyright © 2008 by the American Academy of Pediatrics.