Reviewing the cases published in the literature and studying his own material (3 cases of Surge-Weber-Dimitri's disease, one case of aneurysm of the medial cerebral artery and 5 cases of arteriovenous fistula) by the clinic, the EEG, the roentgenogram and the arteriogram, the author shows the importance of the EEG record in the establishment of correct diagnosis and in the choice of treatment in these cases. The author concludes: 1) In the cases of arteriovenous fistula, the EEG showed focal signs in 4 cases; in 2 of them, the EEG record demonstrated the necessity of arteriograms, for the patients have had one and two seizures, respectively, bringing out the possibility of etiological diagnosis and surgical treatment. In another case, the EEG gave orientation for the diagnosis; the 55 year-old patient had been considered as an epileptic for 25 years. In the fifth case (the aneurysm was small and located between parietal convolutions) the EEG did not show focal signs. 2) In the case of aneurysm of the medial cerebral artery, located in the base of the brain, the EEG revealed diffuse and bilateral signs, probably due to the previous subarachnoid hemorrhage. 3) In the 3 cases of Sturge-Weber-Dimitri's disease, the EEG showed records with depressed electrical activity, corresponding to the calcified areas. In one case the EEG also revealed the presence of a frontal focus which explained very well the Bravais-Jacksonian seizures and the hemiparesis, independently of the occipital angiomatous calcification.