Composer Bernard Herrmann became infatuated with Geneviève Bujold after seeing her performance in an early cut of "Obsession". His feelings were heightened by Bujold's surprise visit to the soundtrack recording sessions in London in July 1975, the only time the two met in person. Herrmann's friend Charles Gerhardt recalled, "As she spoke to Benny in a heavy French accent I could tell he was about to get the hanky out. She told him of all the trouble she'd had with Cliff Robertson because he spent all his time in makeup and didn't make their love scenes meaningful. She said, 'Mr. Herrmann, he wouldn't make love to me - but you made love to me with your music'. And Benny started to cry. He would tell that story over and over at dinner, and start crying again every time". After Herrmann's death five months later, his widow found a photo of Bujold in his wallet.

Geneviève Bujold has no dialogue when playing Elizabeth Courtland, to cover her French accent. When playing Sandra, her accent is passable as Italian.

Alfred Hitchcock was reportedly furious when Brian De Palma decided to make Obsession (1976), because he thought it was a virtual remake of Vertigo (1958).

The second and final Brian De Palma film with music by Bernard Herrmann. Herrmann was slated to score De Palma's Stephen King adaptation "Carrie" (1976) but died before production started.

The church seen at the beginning of the film, Church of San Miniato, is different from the one that Michael actually goes into when he sees Sandra. The reason for this is because the priests of the Church of San Miniato would not allow De Palma and his crew to film inside of the church, because of a previous film crew that turned out to be making a porno film, and had told them otherwise. This can be seen clearly when Michael goes into the church, which only has one door to enter into, and then in the next shot, where Michael's back is towards the door, and there are now two, and a windows on the doors that don't match the one that we saw on the outside shot. The collegiate church in the town of San Gimignano was used for the interior shots.

Brian De Palma's older brother Bart painted the portraits that appear in the film.

According to Brian De Palma in the DVD interviews, when Bernard Herrmann watched Obsession for the first time, he knew exactly how the music score would sound.

According to Brian De Palma, Cliff Robertson was very difficult to work with.

Original title of the film was "Déjà Vu".

When Brian De Palma was filming Obsession in Italy, Martin Scorsese visited the set.

The first Brian De Palma film shot by cinematographer Vilmos Zsigmond.

Cliff Robertson's onset behaviour caused considerable friction. In the documentary "DePalma", Brian dePalma recounts that Robertson would deliberately deliver a poor performance and line readings when shooting reverse shots for Genevieve Bujold. He insisted on a dark tanning makeup, inappropriate for his troubled character. It made lighting him so difficult that at one point cinematographer Vilmos Zsigmond shoved him against a wood wall and shouted "You! You are the same colour as this wall!"

The church in Florence significant in the plot of the film is the Church of San Miniato, or San Miniato al Monte (Saint Minias on the Mountain), a Romanesque basilica built in 1018, on the site of a 4th century chapel.

The first Brian De Palma movie filmed in New Orleans, LA.

One of his final scores, Bernard Herrmann personally considered his work for this film to be his best.

The first Brian De Palma movie filmed in the 2.35 : 1 widescreen format.

It was Bernard Herrmann who insisted to remove the final part of the film. In the original script, Michael Courtland (Cliff Robertson) kills Robert Lasalle (John Lithgow) and goes to Jail. Michael spent years in jail. When he got out, he travels back to Italy and he travels back to the church and there he sees his daughter who is in a sort of catatonic stage. And the priest who is at the church tells Michael that the only way to get her out of this catatonic stage is to restage the kidnapping yet again with real money and he does. And she comes back from her state and embraces her father. Brian De Palma said that it would have made the movie 3 hours if the entire script were shot. It was Bernard Herrmann who insisted to remove these elements which led to the released version. According to De Palma, Bernard Herrmann said "Well that stuff the future just get rid of it. It doesn't work. They get together in the end." Brian De Palma also said "I think he was feeling musically there was something that would be difficult to recapitulate in the future again."