BackgroundECT is rarely used as a prophylactic treatment. A 74-year-old woman with unstable bipolar affective disorder receiving maintenance ECT presented a unique opportunity to measure the cognitive effects of continuing ECT.MethodA single case report with serial psychometric testing during over 400 ECT treatments as a single maintenance treatment.ResultsSerial testing did not demonstrate progressive cognitive deterioration, but consistent cognitive deficits typical of acute treatment were evident. The degree of cognitive difficulty may be related to the frequency of treatment.ConclusionsMaintenance ECT can be an effective prophylactic treatment for selected patients. Cognitive effects would appear to be no greater than with acute treatment and seem to be non-progressive.