In lambs, acute and chronic communicating hydrocephalus has been created by merely increasing the amplitude of the intraventricular cerebrospinal fluid (CSF) pulsations, leaving the mean CSF pressure unchanged. The pathologic changes occurring in this type of hydrocephalus do not differ qualitatively from those observed in obstructive hydrocephalus. Beside demonstrating a direct role of ventricular pulsations in the ventricular dilation, the observed findings indicate that an increase in mean CSF pressure is not a necessary condition for the occurrence of the hydrocephalus. Consequently, the hypothesis of abnormal high intraventricular CSF pressure oscillations at the basis of the ventricular dilation of normal pressure hydrocephalic patients, receives a significant support. Further support is provided is provided by considering the recorded experimental pathological lesions are quite similar to those observed in normal pressure hydrocephalic patients with patent subarachnoid CSF pathways.