Third ventriculostomy for acquired non-communicating hydrocephalus is an excellent alternative to shunting procedures. Nevertheless, complications can be severe and even fatal (e.g., lesion of the basilar artery), especially if the floor of the 3rd ventricle is very tough and/or opaque. The authors describe a safe method of sharp perforation of the floor, which should be applied if blunt fenestration cannot be achieved easily.