Aim:This multicenter study aims to evaluate the incidence of anatomical variations and abnormalities of the third ventricle floor encountered during endoscopic third ventriculostomy (ETV) procedure in myelomeningocele associated hydrocephalus (MAH) cases.Material and Methods:A retrospective analysis was performed on 455 pediatric MAH cases that have been treated with ETV. This case series consisted of the patients who were initially treated with ETV and those who were treated with ETV for the management of cerebrospinal fluid shunt dysfunction as well. Reviewing the video recordings of the ETV procedures, variations and anomalies of the third ventricle floor were determined. Results:The analysis of the data revealed that, the rate of the MAH cases with variations and abnormalities of the third ventricle floor was 41.1%. The most common anatomical features were—‘’thick and prominent massa intermedia”— (37.1%) and —“narrow tuber cinereum”— (33.1%).Conclusion:This study documents the most common anatomical variations and abnormalities of the third ventricle floor in cases with MAH. Various anatomical situations and specific ventricular configuration of MAH cases may add an operative factor of difficulty which should be well recognized by the neurosurgeon who indicates and executes an ETV procedure in this patient population.