An overview of significant research results of the last four decades as well as the author's own experience have served as a basis for the presentation of the radioisotope method and the radiopharmaceuticals in the diagnostics of normal pressure hydrocephalus (NPH). Also the physiology of the formation of PM-R its flow and absorption have shortly been discussed. Hydrocephalus is a major clinical, diagnostic and therapeutical problem. In the initial diagnosis of that pathology, methods like CT and MRI play an important role, which has also been the subject of this article. A clear and useful classification of hydrocephalus has been presented as well as NPH in adults as a clinical pathological syndrome together with its etiology, diagnostics and the differentiation in relation to other forms of hydrocephalus. Hydrocephalus and the atrophy of the brain have been illustrated by images taken by the author. In the assessment of the NPH in terms of a patient's qualification for a shunting operation a number of diagnostic factors are of particular importance. These are: the infusion test using PM-R pressure measurement of the ventricle system or the subarachnoid space on the spinal cord level, the neuropsychological evaluation as well as the brain imaging using emission tomography SPECT or the measuring of the brain metabolism by PET technique. None of these methods has been universal in diagnostic terms. Radionuclide cisternography seems to be the most physiological method that allows to gain more direct insight into the dynamics and the PM-R flow and its absorption. The results of the radioisotope examination turn out to be the most reliable criterion in the diagnostics of NPH.