The study of 120 arteriograms of patients with the proved nonexistence of intracranial space-occupying lesions, permitted to recognize various forms or normal carotid syphon. It was thus possible to make an anatomic classification of the various types and conclude that the syphon's form alone does not permit the topographical diagnosis of intracranial tumours. It is important to recognize exactly the syphon's form in order to locate precisely the internal carotid aneurysms.