The cathedral of the island, situated in the centre of Platanos, the capital of Leros, dominates the old, commercial street, and is dedicated to the Annunciation. Its reconstruction was completed at around 1860 – 1862.

It is a three-nave, cross-in-square church with dome. It has two belfries that were added later, after 1952, when Isidoros Aidonopoulos was Bishop of Leros, Kalymnos & Astypalaia, to replace the old belfry that had collapsed during the earthquake of 26 June 1926, which caused many damages in the Dodecanese. On its western side, there is a matroneum and a narthex.

The church was renovated – restored in two phases. The first one begun in 2007 and was completed a year later. The exterior of the church was restored and important interventions were made to reinforce the monument, repair the damages the building had suffered over time and insulate the cracked roof through which humidity would penetrate it and damage the coatings of the church interior. On the inside, the church (walls, columns, etc.) was painted with green oil-paint in various shades. The top of the columns had more modern, plaster capitals painted in golden paint, and the arches and other elements were decorated with flower features dating back to 1970, and, sometimes, murals dating back to 1975, most of them completely worn because of the humidity.

The church committee, further to suggestion and with the blessing of the acting Bishop Mr. Paisios, approved and proceeded to the second phase of restoration, on the church interior, with the aim of repairing the extensive damages, which made even the use of the church dangerous. Works begun in October 2013 and finished six months later, in March 2014. The removal of the old coating revealed construction elements of unique beauty and craftsmanship, such as carved stones and bricks placed in the Byzantine style. Four arches create a peripheral carved base, on which lies the dome of the church. A similar, carved crown in the shape of frame, decorates the dome over the single-lobe windows, the vaults of which are made of bricks. The dome is decorated with a Renaissance-style mural of Christ Pantocrator, by painter of Kalymnos, Antonios Karafyllakis. The spherical arches, on the basis of the dome, are made of bricks, and the four Evangelists, on canvas, also of Renaissance style, are perhaps his works as well. The excellent fitting of the stone frames on the ten columns and their rectangular bases is remarkable. The capitals are of Doric style, but, unfortunately, their corners were destroyed, probably later, when the plaster ones were placed. Half a meter below the base of the capital, there used to be a protruding crown of the same material, which, was, unfortunately destroyed, probably when the columns were coated; it was the same as the one on the base of the column, which has been saved. The same frames were used in all arches between the columns, while the entire central nave of the church, above them, is decorated by a frame of hollow carved stone, many parts of which have been destroyed. The base of the wood-carved pulpit is also splendid. At that particular point of the third column of the left side of the church, the protruding frames form a reverse cone, decorated with reliefs. All the groin vaults of the naves and the matroneum of the church are made of Byzantine bricks, in perfect chromatic harmony with the general appearance of the church, which are preserved in excellent condition. A construction similar to that of the groin vaults is also observed on the semi-vaults of the Holy Altar niches made with off-white to deep red bricks. The circular staircase of twenty stairs, leading to the matroneum, is a masterpiece of construction art. Before its restoration, it was covered with several layers of lime coating, but, after meticulous cleaning, these remarkable architectural elements were revealed. Each step is a piece of carved stone, the perimeter of which was built-in, its centre forming a ring, while all of them were connected between them, probably by lead (according to the technique popular at the time).

After the end of the construction works and the detailed cleaning of the space, the wooden icon screens of the Episcopal Throne and the Pulpit were restored. They date back to 1912 and were constructed by woodcarver G. Tsimetas

On the day of inauguration of the church, the protecting icon of the Holy Mother of God, which until that time, was placed in front of the icon screen, was moved to a new stand, opposite the Episcopal Throne.

Finally, it must be mentioned that the extensive renovation and restoration works of the Holy Cathedral of Leros, is a work of the people of Leros, who, right from the start, showed its love and supported this effort financially or by offering personal work. Forty five pious locals offered volunteer work, in various stages of the renovation, not sparing time or effort, so that the project is completed.

With the help of God and Mary, Mother of God, Protector and Curator of the island and the parish, the presence and help of whom was unremitting throughout the works, the renovation was completed, for the most part, and the Cathedral of Leros was delivered and made available for the worship of the Holy Trinity, which deserves all glory, honour and worship.