Type 1 diabetes mellitus (T1DM) is one of the most common chronic diseases in children and is frequently encountered in pediatric surgical practice. The annual incidence of diabetes in the United States is about 1/4000 children, but the worldwide incidence varies markedly by geographic location and ethnicity. Diabetes will be encountered frequently in pediatric surgical practice, and familiarity with the principles of its pathophysiology, treatment, and potential complications is critical for providing optimal surgical care to these patients. Surgery in patients with diabetes is associated with a variety of special considerations and risks. Perioperative care of these patients requires an understanding of the pathophysiology and current treatment of this disease, which are reviewed in this chapter. Surgical planning, preoperative evaluation, and intraoperative and postoperative management are discussed in detail, including principles of glycemic control, insulin management, and nutrition. Relevant acute and chronic complications of diabetes are also discussed.