Greek physician from Cappadocia who practiced in Rome and Alexandria, led a revival of Hippocrates' teachings, and is thought to have ranked second only to the father of medicine himself in the application of keen observation and ethics to the art. In principle he adhered to the pneumatic school of medicine, which believed that health was maintained by “vital air,” or pneuma. Pneumatists felt that an imbalance of the four humours—blood, phlegm, choler (yellow bile), and melancholy (black bile)—disturbed the pneuma, a condition indicated by an abnormal pulse. In practice, however, Aretaeus was an eclectic physician, since he utilized the methods of several different schools.

After his death he was entirely forgotten until 1554, when two of his manuscripts, On the Causes and Indications of Acute and Chronic Diseases (4 vol.) and On the Treatment of Acute and Chronic Diseases (4 vol.), both written in the Ionic Greek dialect, were discovered. These works not only include model descriptions of pleurisy, diphtheria, tetanus, pneumonia, asthma, and epilepsy but also show that he was the first to distinguish between spinal and cerebral paralyses. He gave diabetes (diabetes insipidus) its name (from the Greek word for “siphon,” indicative of the diabetic's intense thirst and excessive emission of fluids) and rendered the earliest clear account of that disease now known.