The bells of Mondoñedo cathedral, alongside booming fireworks, herald the start of As San Lucas at midday. This is one of the most important traditional festivals in Galicia, dating back to 1156, when Alfonso VII granted the town an eight day celebration. The opening address takes place in the evening, attended by the queen of the festivities and the two maids of honour, the sanluqueiro, dignitaries and members of the Festivities Commission, and giants and large-headed figures, who parade to the Municipal Auditorium with a group of pipers.

The As San Lucas festivities are, at heart, a cattle fair. The horse festival opens on Saturday, when the mass in honour of San Lucas is also given, with massive crowds. The cattle competition at the fairground includes a Galician equestrian competition, in the serrada (two-beat) and chapeada (four-beat) gaits, a dog show, and various dog exhibitions at the Municipal Pavilion. The last day of the festivities is known as the day of the maulas, when all products at the fair are sold at half price.

Every day is packed with charanga marching bands, traditional games, and concerts, and there is also a trade fair for agricultural products and machinery.