Studies conducted in the United States and Japan indicate that diabetes mellitus is more common among schizophrenic patients than among the general population. The prevalence of known diabetes was examined in 95 schizophrenic patients aged 45 to 74 years admitted to a long-term care facility in Italy. The overall prevalence of diabetes was 15.8% (95% confidence interval, 12.1% to 19.5%), and increased from 0% in those younger than 50 years, through 12.9% in the 50- to 59-year age group, and to 18.9% in the 60- to 69-year age group, and then decreased to 16.7% in those aged 70 to 74 years. These rates are considerably higher than those reported from population surveys in Italy, and indicate that a higher prevalence of diabetes in schizophrenic patients may be a universal phenomenon. The clinical picture indicated that in all cases this was the common variant of type II (non-insulin-dependent) diabetes mellitus. Diabetes was more common in patients not receiving neuroleptics than in those who were receiving such treatment. There was no association between diabetes and the use of anticholinergic drugs.