Six cases of maintenance electroconvulsive treatment (ECT) in elderly patients with major mood disorders were followed for 1 to 6 years. Documented duration of illness before instituting maintenance ECT ranged from 6 to 53 years (mean +/- SD = 22 +/- 18 years). Measures of effectiveness and safety of maintenance treatment and measures of functional status were prospectively obtained during periods of outpatient ECT administration, and functional status measures were retrospectively obtained for equivalent pre-ECT periods. Such measures included mean frequency of annual hospital admissions and average annual length of inpatient stay, mean scores on standard rating instruments of global functioning and cognitive performance, the average number of prescribed psychotropic medications, and ratings of affect. Some of the authors' findings support the contention that maintenance ECT may help sustain remission in the course of affective illness.