Complications of type 1 diabetes mellitus include acute severe metabolic disorders, infectious diseases, and chronic complications. 1. Acute severe metabolic disorders: hyperosmolar hyperglycemic syndrome, diabetic ketoacidosis, lactic acidosis, hypoglycemia. 2. Infectious diseases: type 1 diabetes mellitus is prone to various infections due to high blood glucose, such as pyelonephritis, boils, carbuncles, ringworm, and so on. 3. Chronic complications (1) Microvascular lesions: diabetic nephropathy, diabetic retinopathy and so on. (2) Macrovascular lesions: heart disease, hypertension, cerebrovascular accident, etc. (3) Neurological complications: central, peripheral and autonomic neuropathy. (4) Diabetic foot. The vast majority of type 1 diabetes is associated with autoimmune diseases. If diagnosed, insulin should be applied under the guidance of a doctor for treatment in a timely manner.