This prospective study began as one of the HCRN’s first studies. We started it to thoroughly and critically analyze the success and complications of endoscopic third ventriculostomy (ETV), which remains the only viable alternative to CSF shunts. Since 2007, the HCRN has performed over 400 ETVs, of which we reported our experience with the first 336 in this presentation. This study has set a landmark as the largest prospective, multicenter study of pediatric ETV to date. The main strength of this study was that we were able to collect, in real time, detailed data about what actually took place during surgery, including the amount of bleeding, how successful the surgeon was in creating the hole in the third ventricle, and if the surgeon saw any evidence of injury to the brain. This level of data has not previously been collected on so many patients. Our results were very comforting. We found that very serious complications are exceptionally rare (well less than 1%) and the overall success rate of ETVs was 66%. When we looked for the important factors that predict ETV success, not surprisingly, the “ETV Success Score” (which accounts for the effects of age, hydrocephalus etiology, and whether the child had a previous shunt) was the most important. Interestingly, many of the factors that surgeons assess at surgery (like how big they were able to make the hole in the third ventricle and whether there was bleeding during the operation) were not significant predictors of ETV success. One of the explanations for this rather counter-intuitive finding might be that, perhaps, there were still too few patients in this study for the statistics to show up “significant”. The HCRN, of course, is continuing this study, which will be an on-going component of the HCRN’s research focus in the years to come.