Annual outbreaks of mass motor hysteria have been observed in the past during some religious celebrations. In Jaca, a Northern Spanish town close to the Pyrenees, the convulsionaries have been well known since the eleventh century, though little attention has been paid to this phenomenon in the medical literature. Pilgrims from remote parts of the valleys gathered in procession on June 25th in front of Saint Orosia sarcophagus. Epileptics, psychotics, the paralyzed and hysterics joined the procession looking for healing together with in exorcist rituals. Reig and Gascó, a military physician, described in 1881 the atmosphere of fervour, ignorance and vestigial paganism accompanying these unusual behaviours. Saint Orosia's convulsionaries ended in 1947 following prohibition by local Catholic Authorities, probably the recurrent outbreak of mass motor hysteria lasting to most recent years in Europe.