ObjectivesManaging symptoms, notably psychiatric symptoms, in dementia with Lewy bodies (DLB) is complex, affecting both patients and caregivers. People with DLB often react poorly to antipsychotics, limiting treatment options. Although electroconvulsive therapy (ECT)'s potential for DLB is acknowledged, evidence is scarce owing to limited studies. This study investigated ECT's effectiveness and safety for DLB and prodromal DLB with antecedent psychiatric symptoms.MethodsThis retrospective study investigated people with DLB (N = 12) and mild cognitive impairment (MCI) with LB (N = 13), a prodromal form of DLB, who underwent ECT for psychiatric symptoms and had abnormal findings confirmed using dopamine transporter single‐photon emission computed tomography and 123I‐metaiodobenzylguanidine myocardial scintigraphy. We reviewed these patients' medical records and determined the severity of psychotic symptoms before and 1 week after the final ECT session with the Clinical Global Impressions Severity Scale (CGI‐S). Improvement in psychotic symptoms was evaluated approximately 1 week after the final ECT session using the CGI Improvement Scale (CGI‐I). Additionally, we assessed cognitive function and dementia severity before and after ECT, as well as any adverse events caused by ECT.ResultsECT significantly improved psychiatric symptoms, as assessed using the CGI‐S, with CGI‐I reports in the order of 60% “very much improved,” 20% “much improved,” 16% “minimally improved,” and 4% “no change.” Parkinsonism improved (Hoehn and Yahr: 1.76 ± 1.2 before vs. 1.04 ± 0.7 after, p < 0.001) as did dementia severity (Clinical Dementia Rating, p = 0.037). Adverse events included delirium in 24% of patients and amnesia in 4% of patients. ECT did not worsen cognitive function.ConclusionsECT for DLB and MCI with LB with antecedent psychiatric symptoms appears safe and effective in managing psychiatric symptoms and Parkinsonism. Further large‐scale multicenter studies are warranted to conclusively establish its effectiveness and safety.