In order to carry off the deception, all of Warren's dialog was actually dubbed in by an (uncredited) male actor.
The dialog makes repeated references to Emily, Warren and Helga being in Denmark. At the time this film was produced, the early 1960s, Denmark was the only place where competent transsexual operations were being routinely performed.
The premiere was held at the Palace Theatre in Youngstown, Ohio with producer William Castle in attendance.
This was one of the most successful knock-offs of Alfred Hitchcock's Psycho. William Castle and Columbia had this in theaters a year after the release of "Psycho". Part of the reason for the delay was that, at the time "Psycho" went into release, Castle was still working on 13 Ghosts.
William Castle:
[gimmick]
In the final reel, when Miriam is about to go into the house for the big climax, there was a one-minute "Fright Break" in which producer/director William Castle advised the audience that anyone too scared to see the climax could go into the lobby and get their money back. For this gimmick, Columbia shipped a cardboard "Coward's Corner" to theaters playing the film. Supposedly, audience members too frightened to see the climax could go to the "Coward's Corner" and wait there until the film ended and the rest of the audience filed past. Apparently no one took the offer.