This chapter discusses the diagnosis, evaluation and management of diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar state (HHS). The classic symptoms of hyperglycemia include polyuria, polydipsia, polyphagia, dizziness, weakness, abdominal pain, nausea, vomiting and altered mental status. Treatment of presumed DKA should begin with rehydration and evaluation for precipitating cause in the setting of a high glucometer reading. Further treatment often awaits laboratory results. HHS is sometimes the result of a precipitating stressor like infection, myocardial infarction, or stroke. In HHS it is believed that the body produces enough insulin to prevent ketoacidosis; however, the state of severe hyperglycemia continues to result in osmotic diuresis, hyperosmolar state, and electrolyte abnormalities. Hypoglycemia can occur as a result of overcorrection of hyperglycemia with insulin drip. Cerebral edema may occur as a result of rapid fluid shifts, particularly in the pediatric population.