Director Dario Argento's original idea was that the ballet school would accommodate young girls no older than twelve years. However, the studio and producer Salvatore Argento (his father) denied his request because a film this violent involving children would almost certainly be banned. Dario raised the age limit of the girls to twenty years but did not rewrite the script, hence the naiveté of the characters and the occasionally childlike dialogue. He also put all the doorknobs at about the same height as the actress' heads so they would have to raise their arms in order to open the doors, just like children.
According to Jessica Harper, since the film was going to be dubbed after principal photography, sound was rarely recorded during shooting. Harper remarked that it was strange to her to be in the middle of shooting a scene and hearing the background sound of a stagehand hammering away on another set in the studio.
In 2008, a remake was announced with David Gordon Green as director. However, in 2014, Green dropped out due to budget concerns and legal issues. In September 2015, filmmaker Luca Guadagnino was announced as the new director with Tilda Swinton and Dakota Johnson added to the cast, although Guadagnino stated in press conferences that his version was a personal interpretation of the original and not a "remake," saying, "It's impossible to remake [Argento's] film."
The film is set in Freiburg (officially known as Freiburg im Breisgau), Germany, but in the English dub, the narrator mispronounces it as Fribourg, a different town in Switzerland. Despite this setting, location filming was done in Munich, and several Munich landmarks are visible in the film, including Königsplatz (where Daniel walks his dog at night) and the BMW tower (where Suzy meets the professor).
Udo Kier's appearance was so rushed for him that he had little time to completely read the script when it was given to him. Since the movie was filmed without sound and was later dubbed, a crew person lying on the ground (behind the stone bench where he was sitting in his scene with Jessica Harper) was telling him his lines as he gave them to her.
In an interview, Jessica Harper said that many of the actors spoke different languages during shooting, mostly Italian and German, and it would make communicating difficult at times. However, since the film would be dubbed into English for American release, it was deemed not to be an issue during filming.
Originally, the film was going to star Daria Nicolodi, who was director Dario Argento's girlfriend at the time and who also wrote the screenplay. Nicolodi ultimately did appear in the film twice; she can be glimpsed in the film's opening sequence that shows Suzy walking through the airport, and she also provides the gravelly voice of Helena Markos.
The exterior of the dance academy, though constructed on a studio lot in Rome, is based on the Haus zum Walfisch (Whale House), a landmark late-Gothic building in the old town of Freiburg im Breisgau, Germany.
The voice heard whispering on the bizarre soundtrack by Goblin is that of Goblin band member Claudio Simonetti. Simonetti stated in interviews that much of what he whispers on the music score was just gibberish.
It is often assumed that, to achieve the rich color palette, the film was shot using the outdated three-strip Technicolor process. This was, in fact, not true. No film made after the mid-1950s was shot using this method. This film was instead shot on normal Eastmancolor Kodak stock, then printed using the three-strip Technicolor process, utilizing one of the last remaining three-strip machines. This issue has been confused somewhat by the fact that, on the 25th anniversary documentary featured in the three-disc DVD set, a discussion of the printing process by cinematographer Luciano Tovoli was followed by a diagram showing a three-strip camera.
Rudolf Schündler, the West German actor who played the role of Professor Milius, could not speak any English or Italian, so in the scene where he talks with Jessica Harper (Suzy) about witches, she could not understand him as he was speaking in German. Harper later quoted that she tried to keep a straight face as not to flub her lines.
Barbara Magnolfi has revealed in subsequent years her belief that Olga was a young witch in training, hence her interest in Suzy, and revealed a scripted but unfilled scene where Olga performed with the Bolshoi the night the students were in town; it was ultimately cut because it interrupted the pacing of the film's climax.
The film was restored in 2016 by TLEFilms Film Restoration & Preservation Services, Germany on behalf of the film's rights owners, VIDEA Spa., Italy, with major funding provided by Eightyfour Entertainment, Germany. The restoration, made for the film's 40th anniversary, uses camera negative elements with intermediate negative inserts as well as intermediate interpositive elements to finally return the film to its complete state, with all missing frames carefully restored on a digital basis and the distinct color palette reinstated using reference film materials.
Joan Bennett's partner (later husband) David Wilde was a fan of Argento's The Bird with the Crystal Plumage (1970) and it was at his urging that Bennett agreed to appear as Madame Blanc despite her objections to the violence in films at the time. Besides Wilde's admiration was the all-expenses paid trip to Italy. Bennett however immediately regretted having said yes after finding the Italian filmmaking process slow and disorganized. One day, in preparing for a scene in which she had only one line, Bennett reported to the studio, had her hair and makeup done, got into costume, all by 12:30 pm but then it was five hours before the scene was actually shot. The one consolation was getting to know fellow cast member Alida Valli who befriended Bennett and Wilde introducing them to the excellent and little known restaurants.
The trivia items below may give away important plot points.
Director Dario Argento was inspired to make this film by stories of Daria Nicolodi's grandmother, who claimed to have fled from a German music academy because witchcraft was being secretly practiced there.
Jessica Harper said in interviews that the most frightening scene in the film for her was the grand finale where everything explodes and shatters around her as she flees the academy. Harper said that the rigged explosions were quite unnerving as they went off close to her.
The film's finale was inspired by a dream that co-writer Daria Nicolodi once had. In the dream she said she had encountered an invisible witch and, most bizarrely, there was a panther in the room with her that suddenly exploded. The dream was written into the film, but it's a porcelain panther that explodes.
Stefania Casini had a difficult time shooting her death scene. Though the "barbed wire" that she falls into was fake, the coils of wire still got wrapped around her tightly and pinched her skin painfully.
This was the only installment in the "Three Mothers" trilogy where the witch is not referred to by her original Latin name; instead, she is referred to by her regular name: Helena Markos. She would subsequently be identified as "Mater Suspiriorum" (The Mother of Sighs) in the sequels Inferno (1980) and Mother of Tears (2007).