Hitchcock did most of the promotion on his own, forbidding Leigh and Perkins to make the usual television, radio, and print interviews for fear of their revealing the plot. Even critics were not given private screenings but rather had to see the film with the general public, which, despite possibly affecting their reviews, certainly preserved the secret.
The film's original trailer features a jovial Hitchcock taking the viewer on a tour of the set, and almost giving away plot details before stopping himself. It is "tracked" with Herrmann's Psycho theme, but also jovial music from Hitchcock's comedy The Trouble with Harry; most of Hitchcock's dialogue is post-synchronized. The trailer was made after completion of the film, and since Janet Leigh was no longer available for filming, Hitchcock had Vera Miles don a blonde wig and scream loudly as he pulled the shower curtain back in the bathroom sequence of the preview. Since the title, "Psycho", instantly covers most of the screen, the switch went unnoticed by audiences for years. However, a freeze-frame analysis clearly reveals that it is Miles and not Leigh in the shower during the trailer.