Objectives: We anticipated that elderly diabetic patients showed different clinical features to that of adult diabetic patients. So, we investigated clinical features and beta cell insulin secretory characteristics of elderly diabetic patients compared to that of adult diabetic patients. Methods: Study population were 160 NIDDM patients who were admitted at National Medical Center from March, 1989 to February, 1991. We investigated clinical features of each group and performed 100g oral glucose loading test and measured blood glucose, insulin, C-peptide for 2 hours at 30 miniute intervals after glucose loading. Results: In each group, there was no significant difference in sex ratio, BMI (body mass index), WHR (waist-hip ratio) and lipid profile. The rates of diabetic macrovascular complications were significantly higher in elderly patients than those in adult patients. In comparison of signs and symptoms on admission, main symptom were polyuria, polydipsia, generalized weakness in adult group but chest pain and change of consciousness were main causes in elderly group. After 100 g oral glucose loading, the response of insulin and C-peptide were delayed in elderly group compared to adult group. Conclusion: We observed that elderly diabetic patients showed different symptoms on admission compared to adult patients. And after 100g oral glucose loading, the response of insulin and C-peptide were delayed in elderly group, despite no significant difference in BMI and WHR.