Parents need to know that Slender Man is a horror movie based on a popular internet meme (a "creepypasta") about a faceless monster that steals kids. It has unsettling, nightmare-like imagery that flashes by quickly, as well as jump scares, teens in peril, and teen girls being grabbed and choked.

After the film was released, Bloody Disgusting reported that Screen Gems had required the producers to meet an R MPAA rating and that several scenes had been cut over fears of public backlash (including several scenes that had appeared in trailers), resulting in narrative and continuity issues in the final film.