Thirty patients over 35 years of age with one or more episodes of carotid TIA lasting less than one hour were studied. No patient had a history of brain disease and each had an EEG followed by an arteriogram. Arteriographical study showed 15 patients to have occlusive disease of the internal carotid artery, and four of these had intracranial occlusive arterial disease as well. An additional three patients had only intracranial occlusive arterial disease. Twelve patients had normal arteriographical studies. The EEGs of nine patients were diffusely or focally slow. Twenty-one patients had normal records. Six of the nine patients with abnormal EEGs had arteriographical evidence of intracranial occlusive arterial disease. Only one patient with extracranial carotid stenosis alone showed an EEG abnormality. In two patients with an abnormal EEG the arteriogram was completely normal or showed insignificant change. These data indicate that the EEG has the capacity to reflect changes in cerebral function not clinically evident in patients with carotid TIAs. Such changes were present in almost one-third of the patients in this study. Most commonly, generalized or focal EEG slowing in patients with the clinical syndrome of carotid TIA is associated with the presence of intracranial occlusive arterial disease. Alternatively, the finding of a normal EEG in such patients would suggest the absence of intracranial occlusive arterial disease, but occurs with equal frequency in patients with stenosis of neck vessels and in patients with no arteriographically demonstrable lesion.