The purpose of this prospective cohort study was to compare the costs of day hospital (DH) care for hyperglycemic crisis in elderly diabetic patients with those of conventional hospitalization (CH). Secondary objectives were to compare these two clinical scenarios in terms of glycemic control, number of emergency and outpatient visits, readmissions, hypoglycemic episodes, and nosocomial morbidity. The study population comprised diabetic patients aged >74 years consecutively admitted to a tertiary teaching hospital in Spain for hyperglycemic crisis (sustained hyperglycemia [>300 mg/dL] for at least 3 days with or without ketosis). The patients were assigned to DH or CH care according to time of admission and were followed for 6 months after discharge. Exclusion criteria were ketoacidosis, hyperosmolar crisis, hemodynamic instability, severe intercurrent illness, social deprivation, or Katz index >D. Sixty-four diabetic patients on DH care and 36 on CH care were included, with no differences in baseline characteristics. The average cost per patient was 1,345.1±793.6 € in the DH group and 2,212.4±982.5 € in the CH group (P <0.001). There were no differences in number of subjects with mild hypoglycemia during follow-up (45.3% DH versus 33.3% CH, P =0.24), nor in the percentage of patients achieving a glycated hemoglobin (HbA) <8% (67.2% DH versus 58.3% CH, P =0.375). Readmissions for hyperglycemic crisis and pressure ulcer rates were significantly higher in the CH group. DH care for hyperglycemic crises is more cost-effective than CH care, with a net saving of 1,418.4 € per case, lower number of readmissions and pressure ulcer rates, and similar short-term glycemic control and hypoglycemia rates