Diabetes mellitus, known as the most widespread disease in the world, along with four other chronic diseases, involves major expenditures and significant human resources for care, thus representing a burden on any type of health care system especially due to its rapid evolution of acute and chronic complications. For the emergency department (ED), the requirements of patients with acute complications of diabetes, determine expenses which are three times higher than those for non-diabetic patients and their hospitalizations are four times more frequent. The acute complications for which patients with diabetes most frequently require the ED are hypoglycemic, hyperosmolar, or ketoacidosis coma as well as alterations of the general condition that is typical of hypoglycemia, diabetic ketoacidosis (DKA), hyperglycemic hyperosmolar state and new-onset hyperglycemia. Hypoglycemia and the Somogyi phenomenon are the most common complications of type 1 diabetes but they can also occur in patients with type 2 diabetes who are treated with insulin through its overdose. DKA can occur in type 1 and 2 diabetes either by administering inadequate doses of insulin or due to the existence of precipitating factors such as stress, acute myocardial infarction, infections, sepsis, and/or gastrointestinal bleeding. Hyperosmolar hyperglycemic status is the most common complication in patients with type 2 diabetes and DKA. Treating the acute complications of diabetes in the ED involves, besides taking immediate measures to assess and maintain vital functions, monitoring patients, assessing blood sugar, electrolytes, urea, creatinine, and bicarbonate, and applying appropriate immediate therapeutic measures for each type of acute diabetes complication.