There has been much argument in recent years about the diagnostic and pathogenetic differences between normal pressure hydrocephalus (NPH) and vascular dementia (Multi-infarct dementia) or Binswanger's disease. We experienced an interesting patient, a 54-year-old male, who had left hemiparesis due to two past attacks of cerebral infarction and possible hydrocephalus had been pointed out by CT findings in 1981. He was seen on May 22, 1982, with the chief complaints of dementia, gait disturbance and urinary incontinence. He had the clinical and pathogenetic features, common to NPH and MID or Binswanger's disease. The followings were observed. These symptoms (dementia, gait disturbance, urinary incontinence) and computed tomographic findings (bilateral ventricular dilatation, periventricular lucency), as is often the case in NPH, are at times similar to those of MID or Binswanger's disease and it is difficult to distinguish NPH from MID or Binswanger's disease. We consider that there are probably many patients who are on the borderline of these three diseases. For treatment, the V-P shunt was very effective in combination with the preceding bilateral STA-MCA shunt but it is not clear whether the preceding STA-MCA shunt was required before the V-P shunt. We believe that the clinical symptoms will not appear until the ventricle is dilated to a critical degree. There was a correlation between the degree of dementia and Huckman number, one of the assessment methods for ventricular dilatation.