Cranial nerve dysfunction, obstruction hydrocephalus, signs of brain stem dysfunction, and signs of a space-occupying lesion in the posterior fossa are presumed to be related to a megadolicho basilar artery, if present. Since there are no large series of patients with such vascular anomaly, a bias in relating symptoms with the presence of a megadolicho basilar artery is not excluded. We therefore studied retrospectively the incidence of megadolicho and dolicho basilar artery on cranial CT-scan of 3332 patients of 50 years and older. Patient records were reviewed for the above mentioned symptoms. 12 out of 22 patients with a megadolicho basilar artery and 2 patients out of 40 with a dolicho basilar artery had one or two of these symptoms. It is concluded that a megadolicho basilar artery can cause cranial nerve dysfunction, obstruction hydrocephalus, signs of brain stem dysfunction, and signs of a space-occupying lesion in the posterior fossa ¹⁾.