The following outline is provided as an overview of and topical guide to diabetes mellitus (diabetes insipidus not included below): Diabetes mellitus – group of metabolic diseases in which a person has high blood sugar, either because the pancreas does not produce enough insulin, or because cells do not respond properly to the insulin that is produced, a condition called insulin resistance. The resultant high blood sugar produces the classical symptoms of polyuria (frequent urination), polydipsia (increased thirst) and polyphagia (increased hunger).