Objective To investigate the features and prognosis of the elderly individuals with severe hyperglycemia during hospitalization. Methods All hospitalized patients with age over 60 or older whose fasting or random blood glucose was greater than 20.0mmol/L in our hospital from Jan 1, 2010 to Dec 31, 2011 were enrolled in this study. The causes, medical management and prognosis of these patients were analyzed. Results The cohort of subjects included 100 participants, including 69 diabetic patients and 31 non-diabetic patients, and had 130 times of hyperglycemia, with 90 times for diabetic patients (69.2%) and 40 times for non-diabetic patients (30.8%). And 91% of them were not hospitalized in the Department of Endocrinology. Infection and acute diseases were the main causes of hyperglycemia. The mortality of patients who died within 3 months following hyperglycemia was 54.0% (64.8% vs 61.2% between diabetic group and non-diabetic group, P＞0.05). The main cause of death was multiple organ dysfuction. There were 27 patients having hyperosmolar state, and the mortality in patients with hyperosmolar state was significantly higher than in patients without hyperosmolar state (70.4% vs 47.9%, P＜0.05). Compared with patients whose glycemic was controlled in more than 2 d, the mortality of patients whose blood glucose were successfully controlled within 1 d was significantly lower (39.1% vs 80.6%, P＜0.01). After treatment, the mortality of patients whose blood glucose remained ≥16.7mmol/L was 100.0%. Conclusion Hyperosmolar state and multiple organ dysfunction significantly increase the mortality. Timely reduction of blood glucose (within 1d) and the level of blood glucose less than 16.7mmol/L help to decrease the mortality.