In the syndrome of adult occult normal pressure hydrocephalus, the benefits derived from ventricular shunting generally have been unpredictable. The reason for the unpredictable results of treatment appears to be a relaxation of the criteria for diagnosis of the syndrome. All five key criteria essential for satisfactory surgical prognosis should be satisfied: (1) a history of mild dementia, apraxia of gait, and incontinence, (2) evidence of progression, (3) diagnostic pneumoen-cephalography, (4) strict cisternographic evidence of block, and (5) EEG evidence of decompensation. It is suggested that the excellent results of ventricular shunting are seen primarily in posterior fossa obstruction with lesions involving the aqueduct directly or indirectly.