When only transverse axial slices of a CT [computed tomography] examination already performed are available, the localization in space of small intracranial space occupying lesions is easy only if a lateral view is available at the same time. In terms of 3-dimensional localization, it is possible to rely on the coordinates of transverse axial sections only if the examination is carried out under stereotaxic conditions. In all other cases, uncertainty concerning the site of the plane of reference of the examination would be too great. The method suggested may be used to identify the site of the plane of reference of a CT examination on a lateral skull X-ray with a margin of error of .+-. 2.degree.. It uses the lateral skull X-ray of the patient examined by CT, the transverse axial slices of the examination and a pre-established template. Once the plane of reference is identified, the lesion may be rapidly reconstructed using 2 other templates. The method has the advantage of being applicable to examinations already carried out and does not prolong the duration of investigations.