Diabetes has been known for thousands of years. Because people with the disease, when untreated, urinate frequently and copiously, the Greeks called this disease diabetes, which means "siphon".

During the seventeenth century the name was added mellitus, which means "sweet." In antiquity, the disease is diagnosed by testing the urine. The sweetness is due to the presence of sugar (glucose) in it. This feature distinguishes diabetes  mellitus, a much less common type, called diabetes insipidus, a condition entirely. This overproduction of this hormone that causes excessive production of urine, sometimes up to 25 liters per day (the normal amount is about one liter.) The natural consequence of this disorder is an unquenchable thirst. It is an extremely rare disease, whose cause is unknown in most cases but may result from brain injury or tumor. The treatment is to cure the cause, if known. If not, it gives the patient an antidiuretic hormone.