Because surgery is a likely event during the lifetime of patients with diabetes, health-care team members need to be aware of the metabolic problems that may occur during the perioperative period. Surgery, especially in the presence of general anesthesia, will produce a diabetogenic response. This is generally due to an elevation of counterregulatory hormones, although endogenous insulin is also suppressed. The excessive lipolysis and ketogenesis that can occur during surgery can have particularly deleterious effects for patients with diabetes. Thus, sufficient insulin must be provided during this period to suppress these catabolic processes. The major controversy regarding surgery and diabetes concerns the route of insulin administration. This article reviews the various treatment options for patients with insulin-dependent and non-insulin-dependent diabetes mellitus, with particular emphasis on the role of insulin. Special situations, e.g., outpatient surgery, coronary artery bypass, and emergency surgery, are also discussed.