Agathonísi is a small Greek island and municipality located at the northernmost point of the Dodecanese in Greece. It is surrounded by many smaller islands and is home to two villages, both inland; Megálo Chorió (“Big Village”), and Mikró Chorió (“Small Village”). The island’s only port is the settlement of Agios Georgios (Saint George), which consists of a few hotels. The island is also locally known as Gaidaro, or by its ancient name Tragea.
The highest point on the island is 209 metres above sea level. This peak is located close to Mikro Chorio. The island covers an area of 13.5 km² and its coastline is 32 km long.
By the 2001 census it had up to 158 residents, 144 of whom lived in Megálo Chorió, and only 14 in Mikró Chorió. The municipality of Agathonisi, which includes the uninhabited offshore islets of Gláros, Kounéli, Nerá, and Psathonísio, has a combined land area of 14.500 km².
Agathonisi has a really important and sensitive ecosystem and along with its neighboring islands, makes part of Natura protected areas, as a valuable shelter of rare birds. It can be reached by ferry from Patmos, Leros, Leipsoi, Samos and Chios islands.