The Endoscopic Third Ventriculostomy Success Score (ETVSS) is based on the clinical features of hydrocephalus except for radiological findings. A previous study suggested that transependymal edema (TEE) as a radiological finding may be a reliable predictor of endoscopic third ventriculostomy (ETV) success in patients of all ages. We aimed to investigate whether TEE on preoperative magnetic resonance imaging can predict ETV success in pediatric patients. Medical and radiological records of all pediatric patients with an initial ETV in our hospital between 2013 and 2019 were retrospectively reviewed. This study included 32 patients with hydrocephalus. The median age at surgery was 10.0 years (interquartile range: 5.6-12.9 years). There were 20 patients in the high ETVSS (90-80) group and 12 patients in the moderate ETVSS (70-50) group. The median follow-up period was 29.0 months (interquartile range: 12.9-46.2 months). The ETV success rate at the final follow-up was 81%. Preoperative brain magnetic resonance imaging revealed TEE in 20 patients and third ventricle floor ballooning in 25 patients, of whom 19 (95%) and 22 (88%), respectively, achieved successful ETV. Patients with TEE had a significantly better outcome than patients without TEE (95% vs. 58%, P= 0.018). Multivariate analysis demonstrated that the presence of TEE (odds ratio 13.6, 95% confidence interval 1.3-137.5, P= 0.027) is a significant predictor of ETV success. In our cohort with a high or moderate ETVSS, the ETV success rate in patients with TEE was significantly higher than in patients without TEE, suggesting that TEE may be a useful predictor of ETV success in pediatric hydrocephalus.