ABSTRACT Objectives Non‐immune hydrops fetalis (NIHF) is the pathological accumulation of fluids in fetal compartments, without maternal isoimmunization. Fetal interventions (e.g. shunting, fetal paracentesis, fetal thoracocentesis, fetal pleurodesis) are used to alleviate fluid accumulations, but the outcome is uncertain because the underlying causes of NIHF vary. We aimed to explore the etiology and long‐term outcome of NIHF after fetal intervention. Methods This was a retrospective review of fetuses with NIHF, defined by the presence of fetal ascites, pleural or pericardial effusion, skin edema or cystic hygroma, or a combination of these features, who underwent intervention at our institution during the period 2012–2021. Clinical surveillance, genetic analysis and viral infection screening were used to define the etiology. Chart reviews and telephone interviews were conducted to assess the long‐term outcomes. Results In total, 55 fetuses were enrolled and 46 cases had final follow‐up data after delivery. Etiology was identified in 33 cases, including four for which the underlying causes were not identified initially using small‐gene‐panel tests but which were later diagnosed with monogenic disorders by whole‐exome sequencing (WES). Twenty‐three cases with follow‐up survived, having a follow‐up period of 2–11 years at the time of writing, of which 17 were healthy. All 11 cases initially presenting as congenital chylothorax survived with favorable outcome. Conclusions The etiologies of NIHF are heterogeneous, and the long‐term (spanning 2–11 years) outcome of fetal intervention varies, according to the underlying etiology, with cases caused by congenital chylothorax having the best prognosis. Genome‐wide tests, such as WES, may be helpful in determining the underlying condition in cases caused by a genetic disorder, and this may affect fetal therapy approaches in the future. © 2023 International Society of Ultrasound in Obstetrics and Gynecology. Linked article: There is a comment on this article by Zhao and Li. Click here to view the Correspondence.