The feast of St. Sebastian is celebrated on a grand scale for eighteen days from January 10th to 27th. The flag hoisting ceremony for the feast on 10th January itself throws a heavenly spell on the participants. Owing to the unmanageable crowding of pilgrims and the resultant confusion on 20th January the feast day of St. Sebastian, the church authorities have instituted another minor feast on the 8th day after the principal feast (Octave). This is known as 'Ettam perunnal'. Of late this feast also has attained as much importance as the principal feast.

On the 18th January at the day dawns and the gates of the basilica are opened and the miraculous statue of St. Sebastian is placed. The ceremonial procession to the beach on 20th January attracts a huge crowd of pilgrims. Thousands of pilgrims, who return from the Sastha temple of Sabarimala throng to this sacred place, and pay their homage to the Saint. They remove their Hacocarpus bead chains at the altar.

On 27th January midnight the basilica doors are closed and the St Sebastian's statue is placed at the safe locker . A small statue of the saint is placed there for 40 days. This marks the end of the Arthunkal perunnal. In 2018, more than 2 lakh persons performed the bow and arrow 'nercha'.