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.
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.
When Brian De Palma was filming Obsession in Italy, Martin Scorsese visited the set.
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.
One of his final scores, Bernard Herrmann personally considered his work for this film to be his best.