OBJECTIVE: The atypical antipsychotic medication clozapine is an effective treatment for refractory psychosis; however, the efficacy of clozapine when used in public mental health programs has yet to be fully characterized. This study assessed the outcome of clozapine treatment in a state hospital. METHODS: The medical records of the first 100 patients to receive clozapine in a state hospital, from six months before clozapine treatment through 18 months of treatment, were reviewed. RESULTS: The patients had chronic psychotic disorders that had responded poorly to treatment with conventional antipsychotic medication. Eighteen months after beginning clozapine, 45 patients were much improved, and 18 were somewhat improved. All except one of the improved patients were continuing clozapine treatment. Forty patients were living in community settings, 59 remained hospitalized, and one had died of an illness unrelated to clozapine. Violent episodes in the hospital decreased during the first six months of clozapine treatment. Thirteen patients had one or two seizures while taking clozapine, 12 of whom successfully continued clozapine treatment. One patient developed agranulocytosis, and one developed leucopenia; each recovered fully after clozapine treatment was discontinued. CONCLUSIONS: Clozapine was an effective treatment for refractory psychotic disorders when given as a part of routine state hospital treatment.