This document provides an overview of diabetes mellitus, including its definition, types, metabolic derangements, clinical presentations, complications, investigations, and management. It discusses the various types of diabetes in detail, along with their characteristic symptoms, causes, and treatment approaches. Acute complications like diabetic ketoacidosis and hyperosmolar hyperglycemic state and their management are summarized. Long-term vascular complications involving the eyes, kidneys, and nerves are also outlined.