Trivia

When Sir Robert first arrives at Castle Sardonicus, the castle is in view in the background. The lighted windows make the castle look like a skull.

Baroness Maude Sardonicus (Audrey Dalton) talks with Sir Robert Cargrave (Ronald Lewis) about the culture in her adopted home of Gorslava and mentions they get magazines and stories from London. She mentions reading the works of "Mr. Conan Doyle," obviously referring to Arthur Conan Doyle, who wrote the Sherlock Holmes stories. Even though this movie is set in 1880, and the first Sherlock Holmes story, A Study in Scarlet, was not published until 1886, Doyle's first published piece, The Mystery of Sasassa Valley, was printed in Chambers's Edinburgh Journal on September, 6 1879 and his first academic article, Gelsemium as a Poison, appeared in the British Medical Journal On September 20, 1879, so the movie's reference to Doyle as a writer published in journals by 1880 is accurate.

The British version of this film was cut by about five or six minutes altogether, and the main cuts were very curious. All references to ghouls and their activities were deleted , including the two important moments in the film where the word is defined. The shot of a girl's face covered in leeches was deleted, despite shots of leeches on a human body had been retained in The African Queen (1951) over a dozen years earlier. All shots of Sardonicus' disfigured face, save for the final one, were also cut.

Ray Russell's original story, titled Sardonicus, was published as a serial in Playboy, of which Russell was the senior fiction editor. The story was spread over three consecutive editions of the magazine.

This 1961 film took several years to reach the British Isles, finally getting a very haphazard release in the first part of 1965. The film was heavily cut for the UK, with the censor imposing a number of deletions which were heavily criticized by the few reviewers who wrote about the film.

William Castle: [gimmick] During its initial theatrical release, attendees were given small white cards with luminous thumbs with which to vote thumbs-up or thumbs-down.