Background:Congenital chylothorax is a rare disease of the lymphatic system within the thorax of the newborn infants. Little is known about its natural course and optimal treatment protocol. The purpose of this study was to describe clinical outcomes in neonates with congenital chylothorax and to determine the risk factors of unfavorable outcome. Method:We retrospectively reviewed the medical records of newborn infants with a diagnosis of congenital chylothorax in neonatal intensive care unit of a tertiary center from Jan. 2007 to June 2017. Antenatal, perinatal, and postnatal information including antenatal intervention, drainage output, respiratory support and other treatment modalities were obtained. The risk factors related to unfavorable outcome, which was defined by death or chronic lung disease (CLD, requirement of supplemental oxygen and/or any positive pressure ventilation for at least 28 days), were determined. Result:There were 45 cases of congenital chylothorax. Antental intervention was performed in 40 paitents (89%). The median (range) gestational age was 35+5 (28+1 – 38+6) weeks and median birth weight was 2,750 (1,250 – 4,572) g. Bilateral pleural effusion was detected in 29 patients (64%) and fetal hydrops was complicated in 28 patients (62%). There were 6 cases (13%) of mortality and 12 patients (27 %) were diagnosed as CLD. Thirty-eight infants (84%) required respiratory support during hospital stay. Forty-two patients (93%) were treated with chest drains. The median (range) duration of chest drain was 15 (0 - 68) days in survivors. Aggressive treatment such as octreotide infusion (n=8) and/or pleurodesis (n=1) was performed in 8 patients (18%), mostly those with bilateral pleural effusion (n=7). The time to achieve a 50% reduction in drainage output did not differ between the patients treated with octreotide and those who did not receive octreotide therapy days ( P=0.30). In multivariate analysis, the risk factors for unfavorable outcome were prematurity, low 5 minutes’ APGAR score and bilateral chylothorax. Conclusion:Prematurity, low 5 minutes APGAR score and bilateral pleural effusion were significant risk factors of unfavorable clinical outcomes in newborn infants with congenital chylothorax. Further well-designed controlled trial is required to clarify the efficacy of octreotide treatment in congenital chylothorax.