We have all heard of type 1 diabetes and type 2 diabetes, but what is type 1.5 diabetes? Type 1.5 diabetes mellitus is a type of diabetes mellitus called “occult late-onset autoimmune diabetes mellitus in adults”, which is thought to be caused by the lack of insulin due to immune destruction of pancreatic islet B cells. Why is type 1.5 diabetes mellitus between type 1 and type 2? Because it is an autoimmune disease of the pancreas and the pathological changes are mainly based on the destruction of pancreatic islet B cells, so it is essentially type 1 diabetes; however, it has the characteristics of obesity and late onset, and the latter is due to the slow progress of pancreatic lesions, which usually develops only in adulthood, and the early stage (within six months to a year) is effective with oral hypoglycemic drugs, unlike type 1 where insulin must be used to control the disease after the onset, which occurs six months to a year later, After six months to a year from the onset of the disease, ketoacidosis can occur despite the use of hypoglycemic drugs, which is also like type 2 diabetes. This is the main characteristic of the so-called type 1.5 diabetes. How should type 1.5 diabetes be treated? It is currently believed that in addition to basic dietary therapy and exercise, the most effective treatment for type 1.5 diabetes, once diagnosed, is immediate treatment with insulin, with the addition of immunosuppressants, such as small doses of cyclosporine A or tretinoin tablets, aimed at preventing autoimmune-mediated islet beta-cell damage, promoting islet repair, delaying the insulin-dependent phase, and reducing chronic complications. and to reduce chronic complications. Generally speaking, doctors will not continue to give patients sulfonylurea hypoglycemic drugs such as euglycemia, because if sulfonylureas that stimulate insulin secretion are used again, they will not only fail, but also cause complete destruction of some remaining islet cells, resulting in more serious damage. It should be reminded that while using the correct treatment plan, patients should frequently go to the hospital to review the function of pancreatic islet beta cells to understand their dynamic changes so that the treatment plan can be adjusted at any time. Patients should also insist on rechecking glutamic acid decarboxylase antibodies once every six months or once a year so that doctors can keep track of their changes. Such regular checkups help in disease control and regression, and can avoid and reduce the occurrence of chronic vascular complications of diabetes on the basis of good glycemic control. Since the clinical manifestations of type 1.5 diabetes look no different from type 2 diabetes, it is very easy to be misdiagnosed as type 2 diabetes, which leads to incorrect treatment and aggravation of the disease. Therefore, those who develop the disease in adulthood, lose weight, and use oral hypoglycemic drugs for six months without success should be alert to type 1.5 diabetes.