In this pilot study, a prolonged (interictal) delirium was induced by electroconvulsive therapy (ECT) in seven out of seven depressed patients with Parkinson's disease. This occurrence of delirium appears much higher than what has been reported in other patient populations. These findings are consistent with several lines of data that have implicated the basal ganglia in the development of delirium from other causes, and they suggest that structural changes in these areas may predispose individuals to develop an interictal delirium during a course of ECT.