The sequence where Darryl slips and falls over on the builder's supplies as he is leaving for work was unscripted, as actor Christopher McDonald genuinely lost his footing. Despite this he remained in character, yelling at the workmen as he got into the car and drove away. As he states on the DVD commentary, director Ridley Scott liked the result so much, he kept it in the film.
The scene where Louise grabs Thelma's headphones off her and scares her wasn't planned. In the DVD's audio commentary, Geena Davis commented that she was supposed to get up when Susan Sarandon called her from the car, but she had the volume on her walkman up too high and didn't hear her cue so Susan came over to get her.
In the scene where the tanker truck is shot and blown up, the reactions of Susan Sarandon and Geena Davis were supposed to be genuine. Rather than filming separate reaction shots, director Ridley Scott rigged the tanker to blow up during the take, in order to get authentic expressions of surprise from the two leads. Despite this, they were so astonished while watching it that they forgot to actually react, so Scott had to film their reactions again.
For the more raunchy sex scenes between Brad Pitt and Geena Davis, director Ridley Scott had assumed that a body double would be needed for Geena. Shortly after he'd begun auditioning prospective doubles, Davis learned of Scott's intentions and insisted that no doubles were needed in those steamy scenes.
Ridley Scott was reportedly so amazed with Hans Zimmer's score that he created a main title sequence (with Zimmer's music over it), rather than giving the main credits at the end as it was primarily planned.
Jason Beghe improvised his scene where the State Trooper starts crying when Thelma's holding a gun on him, deciding it would make his character more memorable instead of merely and unemotionally complying with Thelma and Louise's demands.
According to the DVD commentary, Susan Sarandon explained that when Louise gets out of the car to throw up, egg whites were used for the vomit, and she added that they are also used for love scenes in movies.
Brad Pitt had previously lost the role of a character named J.D. in the movie Heathers (1988) to Christian Slater. He got his revenge when he stole the role from Slater of another J.D. for Thelma & Louise.
Catherine Keener was cast in the role of Investigator Hal Slocumb's wife. Her one and only scene was cut from the final film. This deleted scene can be found on the special edition DVD of the film released in 2003 from MGM Home Entertainment.
In the documentary The Celluloid Closet (1995) (based on the Vito Russo book of the same name), Susan Sarandon said that she added the kiss between Louise and Thelma at the end of the movie. Sarandon said that she told costar Geena Davis (but no one else) that she was going to kiss her.
Ridley Scott is very receptive to ideas from cast and crew members on his films, and used many suggestions from Susan Sarandon during production. Some ideas of Sarandon's that made the final cut of the film: the visual of Louise packing her shoes in plastic bags while prepping for the lady's weekend getaway in the mountains; the scene where Louise exchanges her jewelry for the old man's hat; and the scene where Louise stops the car in the desert at night and takes a personal moment looking at the stars while Thelma sleeps in the car. That last scene idea took half the night to light. Sarandon and her longtime partner Tim Robbins reworked most of the dialog in the sequence between Louise and her boyfriend Jimmy at the hotel in Oklahoma City. Originally that scene called for Louise and Jimmy to make love and conduct an impromptu mock wedding ceremony. Sarandon felt that having sex would be the last thing Louise would be interested in doing at that point in the story and told Scott that if she performed the sequence as written that they would have to include a scene where Louise would wig out as a result. And prior to signing on to do the film, Scott gave Sarandon his word that he would not change the ending of the movie. She had just experienced that on her last movie, White Palace (1990), with the original, ambiguous ending being scrapped in favor of a more upbeat one and did not want "Thelma & Louise" to meet a similar fate.
Ridley Scott filmed a longer ending (found on the Special Edition DVD) in which we see the car plunge into the canyon, with a melancholy B.B. King song playing in the background. Instead he opted for a more upbeat ending with the car frozen in ascent and Hans Zimmer's score playing.