The most likely fatal complications of diabetes mellitus in the elderly include cardiovascular and cerebrovascular diseases, hyperosmolar non-ketotic diabetic coma and so on. 1. Cardiovascular and cerebrovascular diseases: including cerebrovascular infarction, myocardial infarction, coronary heart disease and other diseases, diabetic patients are prone to other metabolic diseases, such as hyperlipidemia, obesity, hypertension, gout and so on, the elderly are relatively more complications, prone to induce acute cardiovascular and cerebrovascular diseases, resulting in serious consequences. 2. Hyperosmolar non-ketotic diabetic coma: mostly seen in the elderly, diuretics, diarrhea, vomiting and other triggers can lead to a sharp rise in blood glucose and blood osmolality, manifested as severe dehydration, often accompanied by impaired consciousness, prone to serious consequences. 3. Others: diabetic ketoacidosis, hypoglycemic reaction, severe diabetic nephropathy resulting in renal failure. Diabetic patients should be under the guidance of a doctor to effectively control blood glucose, to avoid the occurrence and progression of complications.