A prolonged (interictal) but reversible delirium was induced by electroconvulsive therapy (ECT) in 10 of 87 (11%) elderly depressed patients. Brain magnetic resonance imaging (MRI) revealed several structural abnormalities, particularly basal ganglia and moderate to severe subcortical white-matter lesions, in the patients who developed delirium. These findings are consistent with several lines of data that have implicated the basal ganglia and subcortical white matter in the development of delirium from other causes and suggest that lesions in these areas may predispose one to developing an interictal delirium during a course of ECT.