Summary: The study examines the naturalistic clinical course of 21 patients with delusional depression following their acute response to ECT. Their course is contrasted with that of 31 patients with delusional depression who acutely responded to medication treatment. They were treated for a minimum of 6 months (mean 3.5 years) with various continuation medications. Delusional depression is associated with a high rate of relapse, and some form of continuation therapy is clearly required. Akin to the acute treatment studies of delusional depression, prophylaxis with antidepressants alone is inadequate in preventing relapse in delusional depression patients.