Since this was a film by Warner Brothers, much of the soundtrack was stock and is the same as used in their 1942 film Reise aus der Vergangenheit (1942).
The Danvers State Mental Hospital was an actual hospital, one that used treatments such as the lobotomy, electroshock therapy, and drug therapy. In the 21st century, most of the building was destroyed and is now for sale as condo property. The film Session 9 was also shot at the hospital building. In the 1970s the outdated treatments were terminated; they were replaced by community-based mental-health treatment.
The harsh winter in Marblehead, Massachusetts proved to be a problem when filming scenes outdoors. Equipment had to be de-iced often, and actress Rhonda Fleming took frequent breaks, complaining that her tongue was freezing.
Exteriors for the film were shot in Boston, Marblehead, Wakefield and Salem, MA, according to publicity for the film. The author of the best-selling novel, Eileen Bassing, formerly lived in Marblehead, MA, the basis for the fictional "Cape Marble" of the book and film. Additional filming took place in the Crystal Room of the Beverly Hills Hotel, which was used for the hotel in Boston, and at Point Sequit on the coast at Malibu for the scenes by the lobster traps.