We performed a prospective, naturalistic study using standardized clinical rating scales to characterize the effect of electroconvulsive therapy (ECT) on mood, cognition, and medical status in late-life depression. Over a 16-month period, 40 patients aged 60 years and over who fulfilled DSM-III criteria for a major depressive episode received a total of 42 ECT courses. Three patients (7%) developed significant medical complications: one had a syncopal episode due to arrhythmia, and two had symptomatic vertebral compression fractures. Confusion was noted during 13 courses (31%) and persisted at discharge in four (10%). More than half the patients were either psychotic or demented on admission, and all but three had been either unresponsive or intolerant to pharmacotherapy. All patients experienced a decrease in their depressive symptoms and more than two thirds were in complete or partial remission at discharge. Patients with psychotic depression experienced a greater improvement than patients with nonpsychotic depression, and patients with organic mental disorders experienced the same improvement as other patients. This study confirms that ECT is a safe and effective treatment of depression in late life.