Trivia

According to director Umberto Lenzi, both Franco Nero and Fabio Testi were considered for the lead in the film, but the producer insisted on a Mexican leading man to appeal to Mexican audiences. Hence, the role went to Hugo Stiglitz.

Reportedly, the film's abrupt twist ending was because the filmmakers couldn't think of a reasonable way to end the story that wouldn't exceed their already-limited budget.

Famed Italian stuntman and actor Ottaviano Dell'Acqua in a uncredited role portrays one of the zombie-like infected people who also is best remembered for his portrayal as the infamous eye-worm zombie rising from the ground and cover of Lucio Fulci's Zombi 2 (Zombie) (1979). His brother Roberto Dell'Acqua also stuntman, portrays one of the infected vampire-like zombies in a uncredited role as well.

Umberto Lenzi insisted that the film's antagonists should not be considered zombies, because they were "infected people" and not undead ghouls. Despite this, the movie is usually considered a zombie film, including by Quentin Tarantino. During a promotional interview for Grindhouse (2007), Tarantino claimed that Lenzi became very annoyed when he called Nightmare City "a zombie movie" while praising it.

Several scenes feature real members of the Spanish military and police forces as extras.