Glenn Close graduated from Rosemary Hall, an all-girls boarding school, the same year Michael Douglas graduated from the Choate School, an all-boys boarding school. The schools later combined to form Choate Rosemary Hall, which is co-ed.
When Glenn Close finally secured the part of Alex Forrest, one of the first things she did was to take the script to two different psychiatrists to ask them: "Is this behavior possible and if it is, why?"
When Glenn Close's agent first called to express her interest in playing Alex Forrest, he was told, "Please don't make her come in. She's completely wrong for the part." Director Adrian Lyne also thought that Glenn Close was "the last person on Earth" who should play Alex.
During the re-shoot of the ending, Glenn Close suffered a concussion from one of the takes when her head smashed against a mirror. After being rushed to the hospital, she discovered, much to her horror, that she was actually a few weeks pregnant with her daughter; actress Annie Starke. To this day, Close said watching the ending makes her uncomfortable because of how much she unknowingly put her unborn daughter at risk from the physically demanding shoot.
After poor audience reaction to the original ending, it was decided that the ending be re-shot. Glenn Close was opposed to redoing the ending, but eventually felt she owed it to everyone else to do it. (In the November 1996 edition of 'Movieline' magazine, Close said: "The original ending was a gorgeous piece of film noir. She kills herself, but makes sure that his prints are all over the knife, and he gets arrested. He knows he didn't do it, but he's going to jail anyway. But audiences wanted some kind of cathartic ending, so we went back months later and shot the ending that's in the movie now.")
The two psychiatrists who reviewed the script at Glenn Close's request both came to the same conclusion: Alex Forrest's behavior was - in its own way - classic behavior. Their diagnosis was that Alex had been molested and sexually tortured for an extended period of time while she was a child. As such, she would naturally lash out at anyone who found her desirable.
While on a break from filming the fight scene in Alex's apartment, Glenn Close took her dog, Gaby, on a walk around the complex where the production was shooting on-location. Close, still wearing the film's iconic white dress, covered in dirt and sweat, with her hair unkempt, began to notice three girls approach her with curiosity. Thinking that the girls presumed she had just been mugged, due to her appearance, Close was about to explain to the girls that she was only shooting a movie. But the girls were really just interested in meeting her dog.
Producers Sherry Lansing and Stanley R. Jaffe had difficulty getting a studio to green light the film, and in finding a leading man. Michael Douglas was when writer James Dearden was expected to both write and direct. Douglas's experience with another less-experienced directed led him to ask for a different director, but Dearden was still kept on as writer--a rarity in the film business. Brian De Palma agreed to direct it, which got Paramount to green light the film, but he refused to stay on the project unless he could replace Michael Douglas. Lansing and Jaffee had a loyalty to Douglas, who was the first actor to express interest in the part, and who himself had experience as a producer. To keep Douglas on the project, they released De Palma. They had feared Paramount would the cancel the project, but instead they merely delayed the start of production which had, at the time of De Palma's departure, been 10 weeks away.
To get the desired reaction shot from Ellen during the scene where she witnesses her parents have an intense argument, the director was behind the camera bullying her and threatening to take away the stuffed animal she was holding, which is why she begins crying and hugging it tighter. After the director yelled "cut" he immediately apologized to her and said he was only kidding.
The trivia items below may give away important plot points.
The original ending had Alex committing suicide while dressed in white, and Dan being arrested for her murder. It was changed when preview audiences felt that Alex was not brought to justice. This ending still appears in the Japanese release. The ending was re-shot in the worship room of the Unitarian church in Mt. Kisco, NY for three weeks in July, 1987.
Alex's treatment of the pet rabbit has given rise to the commonly used expression "bunny boiler" in the UK - used to describe an obsessive woman with the potential to stalk casual acquaintances or one-night stands.