The article presents an analysis of the mystery vocabulary in the Panarion of Epiphanius of Cyprus, written in 374–377 CE. In this text, the term mysterion refers both to Christian mysteries, the true ones, and to heretic mysteries. From a theoretical point of view, the word has neither a positive nor a negative connotation. Only the context enables us to understand the meaning of these mysteries because, according to Epiphanius, all religions celebrate mystery cults. The aim of the article is to analyse why mysteries form an essential element in the construction of the heretic's image and how Epiphanius strategically uses the negative perception attached to mystery cults against heretics.