The morbidity of hyperglycemic crises and acute hypoglycemic attacks in patients with diabetes mellitus has been increasing for the past several decades. One of the reasons for this is the increase in the number of patients with diabetes. The increased proportion of aging and isolation in society is another reason. The author has discussed patients with these complaints: their epidemiology, pathophysiology, and management in the emergency department. Hyperglycemic crises include diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic syndrome (HHS), and lactic acidosis (LA). Younger patients with type 1 diabetes suffer from DKA; inappropriate insulin therapy or infection is usually the trigger. Older patients with type 2 diabetes are at risk of HHS in the course of sepsis or in the perioperative period. The treatment of both types of patients is common. Sufficient amount of intravenous extracellular fluid and constant infusion of insulin are essential. The development of LA is not associated with the use of metformin, but with the severity of the pre-existing disease. Early recognition and aggressive treatment is vital to improving the prognosis of hyperglycemic emergencies and severe hypoglycemic episodes.