This was the earliest American film to feature extensive location work in Italy involving the principal actors. Whilst filming, Joseph Cotten was invited to lunch by his old friend Orson Welles, who confided that he had also invited a couple of Italian businessmen whom he wanted to invest in his film version of "Othello". The presence of a film star would, Welles hoped, influence them to put up some money. Also in the restaurant was Sir Winston Churchill, whom Welles hailed most affectionately as he walked past. He later admitted to Cotten that he and Churchill had never previously met, but that he was hoping that this, too, would impress the Italians. His strategies worked; they agreed over lunch to help finance Welles's film, and Cotten and his co-star Joan Fontaine even played uncredited cameos in "Othello" whilst they were still filming "September Affair".
When Fontaine's character is at the piano, camera shots that include the actress's face are arranged so that the keyboard is not visible, so that she can mime the motions of playing. When the keyboard is visible and hands are shown playing, the camera is positioned so that Fontaine's face is not seen, allowing a skilled pianist to sit in for her.
In the early 1990s, legendary producer Robert Evans was developing a remake of the movie which was supposed to star Michael Douglas and Julia Roberts. Reportedly, Douglas was very interested in the project and spent a lot of time working on the script with writer David Rayfiel.
"Lux Radio Theater" broadcast a 60 minute radio adaptation of the movie on
Janaury 26, 1953 with Joseph Cotten and Joan Fontaine reprising their film roles.