Primary hydrothorax is a congenital anomaly affecting 1 in 10,000-15,000 pregnancies. The natural history of this condition is variable with some fetuses having spontaneous resolution and others showing progression. The associated pulmonary hypoplasia leads to increased perinatal morbidity and mortality. Optimal prenatal intervention remains controversial. After obtaining the Institutional Review Board approval, a retrospective review of all patients evaluated for a fetal pleural effusion in the Fetal Diagnosis and Treatment Center at The University of Michigan, between 2006 and 2016 was performed. Cases with secondary etiologies for an effusion or when families decided to pursue elective termination were excluded. Pleural effusions were identified in 175 patients. Primary hydrothorax was diagnosed in 15 patients (8%). The effusions were bilateral in 13/15 cases (86%) and 10/15 (66%) had hydrops at presentation. All 15 patients with primary hydrothorax underwent prenatal intervention. Thoracentesis was performed in 14/15 cases (93%). Shunt placement was performed in 10/15 cases (66%). Shunt migration was seen in four patients (40%) and all of these underwent prenatal shunt replacement. Overall survival was 76%. The rates of prematurity and preterm premature rupture of membranes were 69% and 35%, respectively. Fetal intervention for the treatment of primary hydrothorax is effective, and it appears to confer a survival advantage. Both the fetuses and the mothers tolerated the procedures well. Preterm labor and preterm premature rupture of membranes remain an unsolved problem. Further studies are needed to understand the mechanisms behind the development of fetal hydrothorax. Copyright © 2017 Elsevier Inc. All rights reserved.