The title "Las crueles" (in imitation of the classic French "Les diaboliques" by Clouzot) was an imposition of the Spanish distributor at the time of commercially releasing the film. The title originally planned by the director Vicente Aranda, and of clear surrealist inspiration, was "The exquisite corpse".
Due to the film censorship laws in Franco's Spain of the late 1960s, the Spanish dub had to have all scenes of nudity deleted before release. In contrast, the American and British distributors demanded more nudity for commercial appeal. The love scene between Carlos Estrada and Judy Matheson was shot in two different sequences. A toned-down version with little or no nudity for the Spanish release, and a more graphic version for all other releases.
After filming wrapped, Vicente Aranda gifted Judy Matheson with the silver hand charm pendant necklace that her character wore in the film. Matheson still has it to this day and even established a trademark of wearing it in her subsequent films.
This film was one of the most expensive jobs and with greater budget of the director, Vicente Aranda. In addition to a long gestation and legal problems, the director suffered an accident that complicated the work, being necessary to build a stretcher adapted to him so that he could finish directing the project.
As of 2019, Judy Matheson (Esther) and Teresa Gimpera (the Editors wife) are the last living stars of the film.