The Holy Diocese of Symi was founded on April 20, 2004 by decision of the Holy and Holy Synod of the Ecumenical Patriarchate, satisfying a constant request of the inhabitants for an ecclesiastical upgrade. In addition to Symi, which is its seat, Tilos, Halki and Kastelorizo belong to the Diocese.
These remote islands belonged to the Holy Diocese of Rhodes, from which they were cut off then, in order to establish the new Diocese.