Background: Hydrocephalus is defined as an inappropriate increased pressure of cerebrospinal fluid (CSF) within the intracranial spaces with an inappropriate amount of CSF. Endoscopic third ventriculostomy (ETV) is considered an effective procedure that is safe. Purpose: The aim of the current work was to detect the factors those predict success parameters in selecting patients with idiopathic obstructive hydrocephalus as candidates for the ETV procedure at a pediatric age. Patients and methods: A clinical prospective cohort study was conducted at Benha University Hospitals from September 2018 to July 2021. A total of 61 patients with inclusion criteria of idiopathic (congenital) obstructive hydrocephalus of pediatric age (under 18 years old) with and without previous ventriculoperitoneal (VP) shunt insertion were included according to calculated sample size who undergoing ETV with a follow-up period of 6-12 months. All patients were evaluated by pre and post-operative operative MRI CSF flowmetry. Results: Sixty-one patients were operated on, with age ranged from 3 to 120 months, and the median (IQR) was 13.0 (5.5-24). Previous VP shunting was done in 15 patients (24.6%). According to the receiving operator characteristic (ROC) curve, the cut off point for ETV success age was 11.5 months; while the cut off point for ETV success score (ETVSS) was 70. MRI CSF flowmetry detected and measured the size of the ventriculostomy stoma and evaluated the flow direction and stroke volume. Conclusions: It could be concluded that endoscopy has reliable validity and safety in the treatment of idiopathic obstructive hydrocephalus. ETV success predictors are patients' age above 11.5 months and ETVSS ≥70, led to increase validity of endoscopy. MRI CSF flowmetry is safe and accurate method for evaluation of the ventriculostomy stoma.