Up until October 2012, Kohnodai Hospital had introduced clozapine treatment for 55 cases of treatment-resistant schizophrenia. In all cases, previous antipsychotic medication was discontinued the day before clozapine administration began. Of the 55 cases, 45(85%)are continuing clozapine administration, and 40 cases (73%) are receiving outpatient treatment. The average dose of clozapine was 373.1 mg/day (SD : 160.5). Clozapine was administered for a month or more in 51 cases (93%). BPRS scores improved 20% or more in a month's administration of clozapine in 18 of the cases (35%). The average clozapine dose in the improvement cases was 176 mg/day. The average BPRS score had significantly decreased from the baseline at months 1, 3, 6, and 12 after the start of clozapine administration. Of the 33 cases receiving clozapine treatment for 12 months or more, BPRS improved 20% or more in 27 (82%). BPRS improved 20% or more for the first time after clozapine administration within a month in 12 cases (44%), 3 months in 8 cases (30%), 6 months in 5 cases (19%), and 12 months in 2 cases (7%). These results suggest that clozapine should be administered continuously for over 6 months at the least and 12 months if possible to evaluate the efficacy of clozapine treatment. Of the 43 cases receiving outpatient clozapine therapy, the average GAF score improved significantly from the time of ward admission to discharge (20.6 and 42.0, respectively). Clozapine had to be discontinued in 2 cases of leukopenia, 2 cases of neutropenia, 1 case of reduced left ventricular ejection due to pericardial effusion, 1 case of drug eruption, and 1 case of marked hunger. When introducing clozapine for treatment-resistant schizophrenia, it is important to administer it as a monotherapy, slowly increase the dosage to reduce side effects, and achieve a treatment effect at the minimum required dosage.