The essay is dedicated to the analysis of the building of the US TV series X-Files, a real end-millennium cult, in multimedia franchise, with a particular attention to its film expansion. First of all, the deeply innovative character of the series is discussed, both on a writing style plan and on that of its relationship with its everexpanding fandom in its on-line community form, complementary to the strong growth of the web in the same years. An attempt is made to propose a taxonomy of the possible strategies of film adaptation of TV series, in the light of the changes in the Hollywood ecosystem and of the new logic of multimedia conglomerates. This is done to frame the particular case study, including two movies realized at ten years’ distance from each other, in completely different situations for what concerns the relation between the series and its franchise, and the social-cultural imagination of the period. Allowing the explosion of the differences between the two film versions, hidden behind the apparent common adhesion to the narrative and formal codes of TV series, it is possible to highlight the peculiarity of X-Files, tracing a possible diachronical path of the relations between TV and movie narration in the last decade.