Hyperglycemic emergencies, such as diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar syndrome (HHS), represent significant metabolic decompensations requiring prompt recognition and management, particularly in oncology patients who have unique risk factors and are at higher likelihood for complications. A comprehensive history of medication exposures is particularly important in cancer patients as chemotherapy, immunotherapy, and other cancer-related treatments are often the cause of hyperglycemic emergencies. Comprehensive history, physical exam, and review of laboratory findings are important in discerning a diagnosis of hyperglycemic emergency from other clinical conditions in cancer patients that may present similarly. Hydration, insulin therapy, and electrolyte management are key components of management of diabetic ketoacidosis and hyperglycemic hyperosmolar state. Proactive counseling of patients with known diabetes and frequent monitoring of glucose during cancer treatment may help prevent hyperglycemic emergencies in this patient population. In this chapter, we will review the epidemiology, risk factors, pathophysiological mechanisms, diagnosis, and treatment modalities for hyperglycemic emergencies in the oncology population.