BackgroundHydrocephalus is commonly associated with Chiari malformation (CM) particularly CM type II. The traditional treatment of hydrocephalus in these patients has been cerebrospinal fluid diversion by shunts. Endoscopic third ventriculostomy (ETV) has emerged as an alternative procedure in these patients.PurposeAssessment of the clinical and radiological outcomes of ETV in the management of hydrocephalus in children with CM II.MethodsThis is a prospective study conducted on 18 patients with CM II associated with hydrocephalus admitted to Cairo University hospitals between January 2020 and June 2021. These patients had been managed surgically by ETV. Clinical outcome was assessed based on improvement of manifestations of increased intracranial pressure while radiological outcome was based on the findings of postoperative computed tomography. In cases with early failure, serial lumbar puncture (LP) was performed for 2 days.ResultsETV was performed as a secondary procedure in 4 cases. The overall success rate of the procedure was 72%, and its success rate as a secondary procedure was 100%. Serial LP was effective in decreasing early failure in 44.4% of cases. Radiological regression of hydrocephalic changes was detected in 50% of the cases.ConclusionETV is an efficient and safe procedure in the treatment of hydrocephalus in children with Chiari malformation II, particularly when performed as a secondary procedure. Serial LP following the procedure increases the success rate in patients with early failure.