Area 13.5 sq. km.
Permanent population 152 inhabitants
Agathonisi is the northernmost island of the Dodecanese complex.
In ancient times it was called Yetousa, while Thucydides calls it Tragaia, Strabo Tragaii - as he includes it together with the adjacent islands and rocky islets that surround it (Kunelonissi, Katsagani, Neronisi, Strogyli, Pitta etc.) and Plutarch Tragia .
Younger travelers refer to it as Agatonissi.

Its current name, which has been used for the last fifty years or so, stems from the good-natured character of its inhabitants, and the text of the renaming of the island was signed by all the inhabitants. Another version says that the name of the island is due to Agathochortos which is often found on the island.

During the prehistoric period it was inhabited by Cares. The Ionians of Miletus followed and later the Dorians.
With a gold bullion of Duke Angelos of Komnenos, Agathonisi is donated to the Monastery of Patmos. Until the 14th century AD it was a hiding place for pirates, while in 1522 it came under the rule of the Turks.
The newest settlement of Agathonissio was made by Patmios and Fourniotes at the beginning of the 19th century. In 1912, the Italians succeeded the Turks and on March 7, after the integration of the Dodecanese into Greece in 1948, it was administratively subordinated to the Municipality of Patmos. In 1954 it became an autonomous Community.
Its shape resembles a donkey, which is why some of its older names were Gaidaros or Gaidouronisi.