The acute and chronic complications of diabetes account for the morbidity and mortality associated with this disease. Acute complications include diabetic ketoacidosis, hyperosmolar hyperglycemic nonketotic coma, and hypoglycemia. Chronic hyperglycemia is central to the pathophysiology of chronic complications such as cardiovascular and peripheral vascular disease, retinopathy, nephropathy, and neuropathy. Pathophysiology and assessment of, and interventions for these complications are discussed.