The film forgoes the more popular (and 20th century) myth that a person bitten by a werewolf will become one. Instead, it invokes the much older idea that a child born on Christmas Day will be the victim of the lupine curse. In many European countries, it was believed that such a child was competing with the assumed birth of Jesus Christ and that the curse was a punishment for blasphemy.
According to the documentary "Flesh and Blood: The Hammer Heritage of Horror (1994)" the Spanish setting for this film was forced upon writer Anthony Hinds after Michael Carreras had the studio back-lot dressed for a film about the Spanish Inquisition. This film was not produced because the Catholic League of Decency threatened to ban it.
This is the only werewolf film made by Hammer Studios.
In an interview, Richard Wordsworth stated that in the original screenplay his beggar character was a werewolf. Hammer Studios told him that the censor had problems with the notion of a werewolf/rapist, so out it went.
Before being released, the B.B.F.C issued Hammer Films with an ultimatum. The film company could present their movie "Curse of the Werewolf" with scenes of either sex or violence but not both.