What is the difference between diabetes insipidus and mellitus?

Unrelated conditions. Diabetes mellitus (dm) is a condition of excessively high sugars which can cause one to void large amounts of urine frequently. Type 1 dm is caused by pancreatic failure so Insulin is required. Type 2 dm is resistance to Insulin or inefficient use. Diabetes insipidus is voiding large amounts of urine frequently due to either kidney or brain disorder, both unrelated to sugar & insulin.