The use of the endoscope in the treatment of hydrocephalus promises a distinct advance in the surgical attack on this condition. By means of the ventriculoscope it is possible to carry out rational surgical procedures with a minimum of shock which was impossible with the earlier forms of surgical intervention. HISTORICAL NOTE Sound surgical principles for the treatment of both types of hydrocephalus were established over a decade ago, largely through the brilliant contributions of Dandy1; but general interest and the practical application of these principles to clinical problems have lagged seriously since that time, as revealed by a brief résumé of the literature. Excision of the choroid plexus as a means of treating nonobstructive hydrocephalus was first proposed by Dandy in 1918.1dAt this time he had successfully performed the operation on four infants. Three died within four weeks, but one was alive after ten months. Dandy,