The increasing prevalence of diabetes mellitus in the general population has many implications for the ambulatory anesthesia provider. Complications, particularly associated with poor glycemic control, can affect multiple organ systems and jeopardize the safety of any planned anesthetic. It is essential that anesthesiologists and sedation providers have in-depth knowledge of the pathophysiology of diabetes mellitus and the comorbid conditions that commonly accompany it. Anesthesiologists and sedation providers must also understand certain surgical and anesthetic considerations when planning an effective and safe anesthetic for diabetic patients. This is a 2-part series concerning perioperative glycemic control for patients with diabetes mellitus. Part 1 will focus on the physiology of diabetes and its associated disease states. Part 2 will address the pharmacology associated with the wide variety of medications used to treat the disorder and the most recent guidelines for blood glucose management in ambulatory surgical patients.