If diagnosed with diabetes mellitus, young age and significant family history of diabetes mellitus, we need to screen for monogenic diabetes mellitus. These include: 1. neonatal diabetes; 2. juvenile onset adult-onset diabetes (MODY); 3. mitochondrial diabetes; 4. severe insulin resistance diabetes. First, the age of onset is particularly young. Some infants are found to have diabetes within six months, and this is likely to be monogenic diabetes, which can also be called neonatal diabetes. Children with neonatal diabetes are often born with low birth weight. Second, there is a clear family history of diabetes. In other words, if diabetes has been in the family for several generations, it is important to be aware that this type of patient may have monogenic diabetes. Third, the age of onset is relatively young, but diabetes typing cannot be determined. Some patients who are considered to have type 1 diabetes but are negative for diabetic autoantibodies and do not have low levels of islet function (C-peptide test) may have monogenic diabetes. Or some patients diagnosed with type 2 are not fat and have too early an age of onset, which may also be monogenic diabetes. Fourth, there is both a family history of diabetes and other abnormalities of the genitourinary tract in those with polycystic liver and polycystic kidney. These patients need special identification and are also likely to have monogenic diabetes mellitus. Fifth, diabetes progresses slowly, with mild or insignificant symptoms, without insulin therapy within 2 years, and without the occurrence of ketosis. Sixth, patients with gestational diabetes present with persistent fasting hyperglycemia and mildly elevated postprandial glucose at OGTT (elevation less than 3 mmol/l). Seventh, severe insulin resistance: fasting insulin > 150 pmol/L (0.87ug/L), peak insulin after sugar load > 1500 pmol/L (8.7ug/L); may have obvious acanthosis nigricans.