A detailed analysis of the deformities of the subarachnoid cisterns was carried out in a clinical material of 65 cases with cerebellar tumours examined by encephalography. The distortion of the cisterns was related to 8 different tumour positions, and the results compared with those from a previous experimental investigation. Typical cisternal distortions for cerebellar tumours are listed, constituting a basis for a general analysis of the cisternal abnormalities demonstrated by whatever means of neuroradiologic procedure employed: pneumography, computer tomography or cisternography with positive contrast medium.