鈥� Serial EEGs with early and progressive bilateral periodic activity were recorded from a patient with clinically "atypical" but pathologically confirmed subcortical arteriosclerotic encephalopathy (Binswanger's type). This disease should be considered as a diagnostic possibility when periodic EEG activity is encountered, particularly when dementia, hypertension, and focal neurologic signs coexist. At times, white matter lesions may contribute to the production of periodic EEG activity.