Absyrtus, or Apsyrtus (Ancient Greek: Ἄψυρτος) can refer to two different figures in classical history and mythology: one was a mythological son of son of Aeëtes and a brother of Medea and Chalciope; the other was a historical, renowned veterinary surgeon.
In Greek mythology Absyrtus was the son of Aeëtes and a brother of Medea and Chalciope. His mother is variously given: Hyginus calls her Ipsia, Hesiod and the Bibliotheca call her Idyia, Apollonius calls her Asterodeia, and others Neaera or Eurylyte. When Medea fled with Jason, she took her brother Absyrtus with her, and when she was nearly overtaken by her father, she murdered her brother, cut his body into pieces and strewed them on the road, so that her father might thus be delayed by gathering the limbs of his child. Tomi, the place where this occurred, was believed to have derived its name from temno (τέμνω, "cut").
According to another tradition, Absyrtus was not taken by Medea, but was sent out by his father in pursuit of her. He overtook her in Corcyra, where she had been kindly received by King Alcinous, who refused to surrender her to Absyrtus. When he overtook her a second time in the island of Minerva, he was slain by Jason. Apollonius of Rhodes presents a variation on this tradition in Argonautica (Book 4): Jason murdered Medea's brother on one of the 'Brygean Islands' (an island sacred to the goddess Artemis and located in the modern Kvarner Gulf), where he was lured by Medea with false promises – their first (and last) meeting after leaving Colchis.
A tradition followed by Pacuvius, Justin, and Diodorus, provided Aegialeus as the name of the son of Aeëtes who was murdered by Medea.
Absyrtus was one of the principal veterinary surgeons of whom any remains are still extant. According to the Suda and Eudokia Makrembolitissa, he was born either at Prusa or Nicomedia in Bithynia. He is said to have served under "Constantine" in his campaign on the Danube, which is generally supposed to mean Constantine the Great, in 322 CE, but some refer it to that under Constantine IV in 671 CE.
His writings are to be found in the Veterinariae Medicinae Libri Duo, first published in Latin by Jean Ruel, and afterwards in Greek by Simon Grynaeus. Christian Konrad Sprengel published a little work titled Programma de Apsyrto Bithynio.