Data concerning to the normal pressure of the CSF at the level of the cisterna magna were reviewed. The values found for 1,500 patients with diseases of the nervous system but without symptomatology of intracranial hypotension or hypertension were analysed. The determination of the pressure was made with the patients relaxed, in horizontal and lateral decubitus. The mean value found was that of 11.9 cm of water and the limits for the physiological variations were 4.1 and 19.7 cm of water. Thus, hypotension is characterized when the pressure is 4 cm of water or lower. Hypertension is to be referred when 20 cm of water or more represents the CSF pressure in the cisterna magna. The CSF pressure is lower in the cisterna magna than in the lumbar region. In a group of 276 patients the mean value found for the later was 16.7 cm of water (lateral horizontal decubitus). The difference between the values showed to be significant. There are not differences related to the sex in the CSF pressure at the cisterna magna. There are significative differences related to the colour of the patients. The values were found to be lower among black and yellow patients. The mean pressure tends to be lower with the age. This tendency was found to increase over 60 years old. The differences related to the colour and to the age of the patients which were found, have not clinical significance.