Between 1955 and 1966 the prevalence of diabetes among hospitalized psychotic women patients rose from 4.2 to 17.2 percent. The increase followed the introduction of chlorpromazine therapy in 1954. About every fourth patient who had been treated for one year or longer with more than 100 mg. daily of chlorpromazine or corresponding doses of another psychoactive pheno thiazine developed hyperglycemia and glycosuria. The disturbance resembled adult-onset diabetes, but there were fewer complications.In 25 percent of the patients remissions occurred either after withdrawal of the drug or reduction in dosage. Obese patients over 50 years old and those with a family history of diabetes were more often affected. Patients with paranoid schizophrenic reaction developed diabetes after phenothiazine therapy relatively more frequently than did those with other forms of schizophrenic reactions or with nonschizophrenic psychiatric diagnoses.