Tilos is situated at the SE Aegean, between Nisyros and Chalki. It is 209 n.m. from Piraeus and 48 n.m. from Rhodes.
In small distance from its shores there are 16 islets with the bigger ones being those of Antitilos in SE and Gaidaros in NW.
The terrain of 62.8 square kilometers in total is hilly consisting of limestone masses with sharp corrugations.
Its coastline is 63 km and it is characterized by steep slopes, cliffs and many bays and coves.
The highest point is the peak of Ai Lias (612 m).
Tilos has springs and an artificial lake fed by the surface run-off of the torrent Potamos, thus in its territory citrus trees and vegetables are cultivated.
The climate of the island is Mediterranean, with mild winters and cool summers.
The island is dominated by shrubby vegetation, while there are trees, mainly olive trees, oak trees, tamarix, and a few plane trees. Chamomile, thyme and sage stand out for their aromas while bellflower, 12 species of orchids (of the genera Ophrys and Serapias), the sea lily and Silybum marianum for their colors. The entire island has been characterized as Bird Protection Zone since 125 bird species have been recorded there, 26 of which are considered strictly protected species (Long-legged Buzzard, Bonelli's Eagle, Phalacrocorax aristotelis, Eleonora's Falcon, Pyrrhocorax pyrrhocorax, Coracias garrulus etc).
Several reptile species live here as well, such as the lizards Ophisops elegans, Cyrtodactylus and Ablepharus kitaibelii and two species of snakes, the Ottoman Adder and the rare Black Coin Snake (coluber jugularis).
The sea life is very rich as well. The Mediterranean seal and herds of bottlenose dolphins approach the coasts. Off of Tilos the rare Aegean Moonfish (mola mola) has been identified while in the depths of its continental shelf lobsters and sponges are abundant.