The study aimed to investigate the effectiveness of maintenance electroconvulsive therapy (mECT) with respect to the hospitalization duration, number of hospitalizations, and major and minor treatment changes with a mirror-image study design. Medical charts of patients who received at least a 3-month-long course of mECT were reviewed. The records of 36 patients (17 with psychotic disorders, 19 with affective disorders) were retrospectively examined for 2 periods with the same duration; during the mECT (post-mECT) and before the mECT (pre-mECT). The hospitalization duration, the number of hospitalizations, and major and minor treatment changes, which were assumed to provide information on the effectiveness of the interventions, were recorded and compared between these periods. Statistical analysis was performed using generalized estimating equation models conducted with age, diagnostic category, and observation time as covariates. In addition, the relapse and recurrence rates and time to relapse/recurrence were analyzed. Comparison of pre-mECT and post-mECT periods revealed that mECT, applied in an individualized schedule combined with pharmacotherapy, was associated with a lower frequency ( P < 0.001; rate ratio [RR], 0.161; 95% confidence interval [CI], 0.087-0.297), shorter duration of hospitalization ( P < 0.001; RR, 0.123; 95% CI, 0.056-0.271), and lower number of major treatment changes ( P = 0.007; RR, 0.522; 95% CI, 0.324-0.840), irrespective of diagnoses. The relapse/recurrence rates were similar in the 2 diagnostic categories ( P = 1.000; 26.3% vs 29.4%). Maintenance ECT should be increasingly considered an important treatment modality in patients with affective and psychotic disorders after an effective course of ECT.