Background: The treatment options for fetal chylothorax include thoracocentesis, thoracoamniotic shunting, and pleurodesis using OK-432. Knowledge on the long-term outcomes after treatment with OK-432 is limited. Objective: The aim of this study was to assess the long-term outcomes of children treated in utero with OK-432. Methods: We performed follow-up on pregnancies and children treated in utero with OK-432 between 2003 and 2009 at Copenhagen University Hospital Rigshospitalet for pleural effusions at gestational age (GA) 16(+0)-21(+6) weeks. Anamnestic information, physical examination, pulmonary function test, neuro-pediatric examination, and intelligence testing using the Wechsler Intelligence Scale were used for evaluation. Results: Fourteen cases, all chylothorax, were treated with OK-432. None had preterm premature rupture of membranes (PPROM), and the median GA at delivery was 38(+5) (24(+4)-41(+5)) weeks. Twelve children were eligible for follow-up. The median age at follow-up was 11.4 (7.8-13.8) years. Pulmonary function was normal in all children and the mean full-scale IQ did not differ from that of normal children. Four children had a diagnosed medical condition, attention deficit disorder, or genetic syndrome. The remaining children had normal follow-up. Conclusion: Children treated with OK-432 have comparable survival rates and long-term neuro-developmental outcomes to those treated with thoracoamniotic shunts. There seems to be a lower risk of procedure-related PPROM. (C) 2018 S. Karger AG, Basel