A review of the 21 cases of "normal" pressure hydrocephalus (N.P.H.) identified by means of radioisotope cisternography, seems to support the basic views of Adams et al. (1965) that a chronic inflammatory disease is an important cause of N.P.H. The clinical and laboratory date made it possible to identify a substantial number of cases affected by N.P.H. in the course of a chronic inflammatory disease; of particular interest were those affected by syphilis. In this connection it seems possible that the symptoms of classical neurosyphilis may be very similar to those often seen in patients with N.P.H.