Endoscopic surgery for obstructive hydrocephalus in children is an alternative to shunts. Currently, the efficacy of endoscopic third ventriculostomy (ETV) in infants up to one year of age is increasingly discussed among neurosurgeons. To increase the efficacy of ETV, many surgeons raise the question: what factors may affect the efficacy of this procedure in the younger age group? Objective — to study the factors affecting the efficacy of ETV. Material and methods. A total of 88 ETVs were performed in infants under one year of age in our clinic in 2012―2016. Subsequently, 43 (48.9%) children underwent CSF shunting, and one child underwent repeated ETV. The mean time until the appearance of clinical signs of stoma closure was 3.9 months (116 days). Results. The procedure was most effective in the case of congenital obstructive hydrocephalus (64.5% of successful operations) and also in children over the age of 6 months (63.6% of successful operations). The efficacy in post-hemorrhagic hydrocephalus was 40%. The efficacy in grade 4 intraventricular hemorrhage was lowest and amounted to 25%. The total efficacy of ETV in children under one year of age in our study was 51.1%. Conclusion. In the case of congenital obstructive hydrocephalus, the efficacy of ETV is maximal and amounts to 64.5%. To achieve the highest efficacy of ETV in infants under one year of age, careful selection of patients at the preoperative stage is necessary, with allowance for many factors affecting treatment outcome.