The International Infant Hydrocephalus Study (IIHS) is a comprehensive cohort study, with both randomized and non-randomized arms, comparing endoscopic third ventriculostomy (ETV) to CSF shunting for infants (age < 24m) with hydrocephalus caused by congenital aqueductal stenosis. It is the largest prospective study to directly compare ETV to shunting in any population. After enrolling patients from 2005 to 2013, accrual was halted by the Data Safety Monitoring Committee due to futility of reaching planned sample size. Treatment failure outcomes (any subsequent treatment for hydrocephalus) were analyzed for all patients and are reported. 158 patients were enrolled from 27 centers across 4 continents. There were 115 ETVs and 43 shunts. After adjusting for age, continent, history of infection or hemorrhage, and stratifying for randomization status, the authors found a hazard ratio of 3.17 (95% CI 1.45-6.96, p=0.004), showing a higher risk of treatment failure for ETV. Subgroup analysis showed that there is a more dramatic difference in favor of shunting in children under 6 months of age, and relatively little difference in children older than 6 months. Final primary outcome is health-related quality of at 5 years and will be reported later. The authors note that the observed rates of ETV success are slightly higher than what would be predicted by ETV Success Score. They conclude that initial ETV is a reasonable alternative to shunting in this population. Of note, only aqueductal stenosis patients were enrolled, limiting applicability to other hydrocephalus etiologies.