Antrum (also known as Antrum: The Deadliest Film Ever Made) is a 2018 Canadian horror film written and directed by David Amito and Michael Laicini. The film is divided into two parts: an opening and closing frame narrative in the form of a mockumentary and a feature film. The documentary purports to tell the story of Antrum, a movie released in 1979 that supposedly has deleterious effects on those who watch it; the bulk of the movie is allegedly the only known print of the film, which has itself been altered by an unknown third party.

Antrum was developed by Amito and Laicini, during the development on a separate project, in which they were brainstorming possible scenarios that they could include in the film. The central idea, that would later become the basis for Antrum, came from the concept of what it would be like to watch a purported "cursed" film, which the filmmakers felt would make for a great horror film. For the film's occult aspects, Amito and Laicini studied various historical and cultural depictions of demons and the devil, while further inspiration came from a short film by David B. Earle titled Dining Room or There is Nothing, which Laicini claimed to have seen while in film school. American actress Nicole Tompkins was cast in the lead role of Oralee, while child actor Rowan Smyth was cast in the role of her younger brother Nathan. Principal photography took place in Southern California, over a period of one month.

Antrum made its world premiere at the Brooklyn Horror Film Festival on 14 October 2018, and was screened at other film festivals, where it was nominated for several awards. Uncork’d Entertainment later acquired North American distribution rights to the film, later releasing it via Video-on-Demand and streaming services in Fall 2019. It received positive reviews from critics who praised its atmosphere, acting, and creativity, while some criticized its pacing, runtime, and plot.