INTRODUCTION: Electroconvulsive therapy (ECT) is a widely recognized treatment for severe depressive disorders, particularly in cases of inadequate response to pharmacological interventions or when rapid symptom relief is essential. Although ECT demonstrates high efficacy, a notable proportion of patients relapse after a successful ECT course. METHODS: This study investigated clinical baseline characteristics and residual depressive symptoms associated with relapse - defined as a Montgomery-Åsberg Depression Rating Scale (MADRS) score >
15, restart of ECT, or suicide attempt - within six months after successful ECT. Data were obtained from the PROTECT study, a single-site, prospective cohort study conducted at the University Psychiatric Center Duffel, Belgium. RESULTS: - Among the 65 patients who completed the ECT course, 40 patients (62%) achieved remission. At six months, 32 patients were reassessed, and 18 (56%) of them experienced relapse. No significant associations were identified between relapse and baseline factors, including age, social circumstances, baseline depression severity, psychomotor symptoms, cognitive functioning, treatment resistance, lithium use, or the presence of psychotic or melancholic features. Residual depressive symptoms at the end of the ECT course also did not predict relapse. DISCUSSION: - The observed high relapse rate underscores the critical need for robust continuation and maintenance strategies following ECT. Future research should prioritize larger cohorts to better identify predictors of relapse and optimize post-ECT treatment protocols.