A brief history of the theories of pathogenesis of the origin of neuroepithelial cysts is presented. An origin more diffuse than the paraphysis seems most likely in our opinion, and we attempt to substantiate this theory with several of the cases from our series. One posterior third ventricular neuroepithelial cyst and one in the fourth ventricle are demonstrated roentgenographically. Also included in our series are a case showing suprasellar calcification on plain skull roentgenograms, not previously reported in neuroepithelial cysts, and a case with a cyst measuring 9 cm, the largest neuroepithelial cyst yet reported.