Schizophrenia is one of the most severe and costliest mental disorders in terms of human suffering and societal expenditure. About 15-30% of patients do not respond to all known antipsychotics, including clozapine, the current gold-standard in these cases. Hence, a recent Cochrane review stated that the quality of the existing studies is too poor to recommend any intervention in addition to clozapine and that new, randomized controlled trials independent from the pharmaceutical industry need to be performed to substantially improve patient care. Although electroconvulsive therapy (ECT) was initially used to treat schizophrenia, it is nowadays by far underused in the therapy of schizophrenia in many countries. ECT is well known to be highly effective in clozapine-treatment-resistant schizophrenia (CRS), and synergistic effects of clozapine and ECT have been demonstrated. However, relapse rates after successful courses of ECT are still very high, and evidence for maintenance ECT (mECT) in CRS is scarce at best. In a multi-center trial the investigators aim to examine the effectiveness of mECT in treatment-resistant patients with schizophrenia who improved after a course of routine ECT. If mECT will lead to a later timepoint of relapse and/or to a higher proportion of relapse-free patients compared to those undergoing treatment as usual, this trial would have an enormous impact on therapeutic strategies for treatment-resistant patients and would induce a profound change of current treatment guidelines, where ECT still ranks at the level of ultima ratio, despite accumulating evidence suggesting otherwise.