 Diabetes is stratified into recognised subtypes with major implications for patients treatment. The treatment of Type 1 diabetes T1D, Type 2 diabetes T2D and Maturity-onset diabetes of the young MODY is markedly different and based on clear differences in underlying pathophysiology. The difficult part of this stratification is correctly diagnosing the subtype especially in young adults. The clear differentiation of T1D as slim and young, and T2D as obese and old, no longer holds with the rapid increase in obesity in the population: T1D patients may be obese and T2D patients may be diagnosed young. 90 of MODY patients are misdiagnosed with T1D or T2D as the diagnosis of MODY is rarely considered. This results in 7-15 of young adults with diabetes being wrongly classified and incorrectly treated. Initial clinical diagnosis is not systematic and once made is rarely changed. Misdiagnosis of T2D or MODY as T1D results in unnecessary initial insulin treatment leading to higher drugmonitoring costs, more side effects weight gain, hypos, and patient inconveniencedissatisfaction. Misdiagnosis of T1D as T2D, or MODY initial treatment diettablets, results in poor glycaemic control, frequent contact for increased treatment, inappropriate insulin regimes and the risk of life threatening ketoacidosis. 