OBJECTIVES: Approximately 30% of individuals diagnosed with schizophrenia suffer from treatment-resistant schizophrenia. Clozapine is underutilized in the management of treatment-resistant schizophrenia. To understand contributing factors, we analyzed the time course and causes of clozapine discontinuations that occurred over a 20-year period in a clinical setting. METHODS: The reasons for discontinuation and duration of clozapine treatment from a retrospective database of 138 patients with schizophrenia who had prescribed clozapine at least a month were reviewed, with the motives for discontinuation coded. The causes for termination were analyzed. RESULTS: Over two-thirds of the patient had ceased clozapine. The two most common causes for discontinuation were side-effects (50%), and own decision (30%). Somnolence accounted for 34% of all side-effects induced discontinuations. Hematological problems accounted for 23% of side-effect. The Maximal treatment dose of clozapine was higher in continuation group (442.36 mg) than in discontinuation group (397.26 mg). The CGI-S score when prescribing clozapine last was higher in discontinuation group than in continuous group. The patients who took atypical antipsychotics before clozapine tended to cease clozapine because of side-effects than who took typical agent. CONCLUSION: Future studies should seek various methods to relieve side-effects of clozapine. Prospective researches using more objective tools are needed to clarify the reason for clozapine discontinuation.