The present study aimed to elucidate the effectiveness of clozapine treatment in reducing the disabling period of chronically ill schizophrenic patients by investigating their rehospitalization status. Of 232 schizophrenic patients with a history of clozapine use who were recruited from the clinic at Seoul National University Hospital, 117 were selected who had been followed up for more than 1 year with respect to rehospitalization. To obtain information about the period before the clozapine change, a chart review of these 117 patients was conducted. The number and length of hospitalizations of the patients significantly decreased after clozapine treatment compared to the same period before clozapine treatment. The hospital days per year of the patients were also decreased significantly after clozapine introduction. By analysing 38 patients who were followed up for more than 5 years, it was suggested that the decrease in the number and length of hospitalizations was substantially sustained for up to 5 years after clozapine treatment. This study showed that the number and length of hospitalizations are significantly decreased by long-term clozapine treatment and that this effect can positively affect the social outcome of schizophrenic patients.