In the light of pneumoencephalographic investigations and radioisotope scinticysternography carried out in 22 patients with clinical manifestations suggesting the syndrome of Hakim the authors analyse the diagnostic usefulness of both methods. In all cases PEG demonstrated dilatation of the ventricular system, in 10 cases radioisotope cisternography showed abnormal passage of the cerebrospinal fluid, and in 8 of these cases ventricular reflux was found lasting at least 24 hours, while in 2 other cases absorption of the cerebrospinal fluid was impaired. On the basis of this material the authors believe that in cases of presence of ventricular reflux this investigation is very important for undertaking the decision of surgical treatment, besides that, the authors think that despite normal scintigraphic pattern in early stage of the disease the investigation should be repeated after from 10 to 20 months, since clinical symptoms may precede disturbances of cerebrospinal fluid passage detectable in cisternographic investigation.