How are diabetes mellitus and just diabetes different?

Old latin term: Type i diabetes, juvenile diabetes is found in children who have lost pancreatic production of Insulin and have poor growth, frequent infections and elevated blood sugar. This may be autoimmune or allergy driven. Type ii diabetes, adult onset, commonly found in patients with Insulin resistance, central obesity and poor exercise habits. The latin term is now shortened to diabetes (type i or ii).

Nothing. : They are actually one in the same. When you hear someone say I have "diabetes" its the short term for diabetes mellitus.