A bad cold, the flu or a serious illness can make blood glucose too high in elderly person with diabetes. Gastrointestinal illnesses may cause hypoglycemia for individuals treated with insulin, sulfonylureas or glitinides. When the persons with diabetes discontinue insulin or diabetes medications because of appetite loss and reduced food intake, they may fall into diabetic crises, such as ketoacidosis, or hyperosmolar hyperglycemic syndrome. The elderly patients need to take extra precautions on sick days to avoid diabetic crises or hypoglycemia. Key principles of sick day management are (1) maintaining hydration and carbohydrate intake, (2) monitoring blood glucose and ketone levels, (3) adjusting diabetes medications according to carbohydrate intake, blood glucose and ketone levels. In Japan, the numbers of frail elderly diabetic patients is markedly increased, effective and efficient sick day management for frail elderly diabetic patients is requested.