Medardus was one of the most honored bishops of his time. His memory has always been popularly venerated, first in the north of France, then in Cologne and extending to western Germany, and he became the hero of numerous legends. His feast day is celebrated on June 8. It is believed that, whatever the weather on his feast day, it will continue for the forty days following, unless the weather changes on the feast of Saint Barnabas (11 June).

He was often depicted laughing, with his mouth wide open, therefore he was invoked against toothache. He is also invoked against bad weather (but also for rain), sterility and imprisonment. He is patron saint of vineyards, brewers, captives and prisoners, the mentally ill, and peasants.