Background . Although diabetes in elderly persons is generally type 2, the metabolic abnormalities associated with aging suggest that elderly persons may differ from younger persons with type 2 diabetes. In addition, nonobese elderly persons with type 2 diabetes show a marked impairment in insulin release accompanied by mild insulin resistance, whereas obese elderly persons have marked insulin resistance in the presence of “adequate” levels of insulin. Other factors that could adversely affect glucose tolerance in aging include drug use, associated disease, and other stressful conditions commonly encountered in geriatric inpatients units. The authors' objectives in this study were 1) to prospectively assess the prevalence of glucose homeostasis abnormalities among elderly hospitalized patients and the degree to which it reflects abnormalities in insulin secretion or insulin sensitivity using homeostasis model assessment of fasting glucose, insulin, and C-peptide; and 2) to define the social, functional, pathologic, and nutritional characteristics of persons with impaired glucose tolerance or diabetes. Methods . Ninety-eight patients underwent a comprehensive geriatric assessment. Determinants of glucose homeostasis were assessed using the homeostasis model assessment, which provides estimates of β-cell function (% B ) and insulin sensitivity (% S ). Results . Twelve patients (12%) had fasting glucose concentrations greater than 110 mg/dl. Four patients had impaired fasting glucose levels greater than 110 mg/dl but less than 126 mg/dl (IFG group), and 8 patients had levels greater than 126 mg/dl (type 2 diabetes group). Except for a higher proportion of women in the IFG-diabetes group, the latter did not exhibit significant differences in functional, morbidity, or nutritional characteristics compared with the normal glucose tolerance group. The entire cohort ( n = 98) presented with a mean (± SD ) % B of 71% ± 47% and a mean % S of 208% ± 198%. Compared with the normal glucose tolerance group, the IFG-diabetes ...