Reports on use of electroconvulsive therapy (ECT) in persons with mental retardation (MR) and mental illness are meager. We describe the successful use of ECT in the management of medication-resistant mental illness in persons with mental retardation. Details of the treatment of five patients with MR and psychotic disorders are reported. ECT was successful after the failure of adequate trials of traditional pharmacotherapy. Persons with MR did not have disproportionate adverse effects of ECT as a consequence of the MR. Four of the five cases reported received maintenance ECT. ECT should be considered in the affective and psychotic disorders occurring in persons with MR when traditional pharmacotherapy fails.