Aim:The aim of this study was to determine the effect of a reduction in the cardiothoracic ratio (CTR) on mortality in newborns with pneumothorax.Methods:Newborns with pneumothorax, who were admitted to our neonatal intensive care unit, were included in the study. The cardiothoracic ratio was calculated by dividing the transverse cardiac diameter by maximum internal thoracic diameter.Results:Of 7909 infants admitted to our neonatal intensive care unit from September 2006 to September 2017, a total of 82 (1.03%) newborns had pneumothorax. Patients who died had a lower CTR than surviving patients (0.39±0.056 and 0.44±0.048, respectively; p