Edward (Richard Gere) snapping the necklace case down on Vivian's (Julia Roberts) fingers, was improvised by Gere, and Roberts's reaction (laughter) was totally natural. The filmmakers liked it so much, they decided to leave it in.
During the lovemaking scene, Julia Roberts got so nervous a visible vein popped out of her forehead. Director Garry Marshall got into bed with Julia and Richard Gere. Marshall and Gere massaged her forehead until the vein disappeared. Julia also broke into hives and was given calamine lotion until they were finally able to shoot the scene.
While shooting the scene where Vivian (Julia Roberts) is laying down on the floor of Edward's penthouse, watching old I Love Lucy (1951) re-runs, in order to achieve a genuine laughter, Director Garry Marshall had to tickle Roberts's feet (out of camera range) to get her to laugh so hysterically.
The movie was originally titled '3000' (after the amount of money Vivian & Edward finally agree upon for her week of service), but later changed to Pretty Woman, after the Roy Orbison track used in the soundtrack.
Richard Gere started off much more active in his role, but Garry Marshall took him aside and said "No, no, no. Richard. In this movie, one of you moves. And one of you doesn't. Guess which one you are?"
During the scene where Julia Roberts sings along to Prince in the bath tub sliding down and dunking her head under the bubbles, Julia came up and opened her eyes and saw that everyone had left even the cameraman (who got the shot).
Burt Reynolds was offered the role of Edward Lewis but declined. He jokingly said on the Piers Morgan show in 2012 that after he saw the film and the love-making scenes with Julia Roberts, that he made a mistake in not taking the part.
In the shots of the city in the very beginning, you will notice that some of the neon letters in the hotel where Vivian lives are burned out. The only remaining lighted letters spell "HO", a slang synonym for prostitute.
According to the DVD director's commentary, the piano key sounds that are made during the lovemaking scene on the piano had to be dubbed in because the actual keys that were randomly hit by Julia Roberts and Richard Gere as they did the scene made such a discordant sound that it was unusable in the actual movie.
The film's budget was not limited, therefore producers could acquire as many locations as possible for shooting on their estimated USD 14,000,000. The majority of the film was shot in Los Angeles, California, to be specific, in Beverly Hills. The escargot restaurant scene was filmed at the Rex, now called Cicada. Filming of the Beverly Wilshire Hotel lobby interior was shot at the now torn-down Ambassador Hotel. Filming commenced on July 24, 1989, but was immediately plagued by countless problems, including issues with space and time. This included Ferrari and Porsche, who had declined the product placement opportunity of the car Edward (Richard Gere) drove, because they did not want to be associated with soliciting prostitutes. Lotus Cars UK saw the placement value with such a major feature film. This gamble paid off as Esprit sales tripled between 1990 and 1991. The company supplied a Silver 1989.5 Esprit SE, which was later sold. The film's primary shooting was completed on October 18, 1989.
Julia Roberts was far from the first choice for the role of Vivian. It was offered previously to many successful A-list actresses including "brat pack" member Molly Ringwald (who starred in Sixteen Candles (1984), The Breakfast Club (1985), and Pretty in Pink (1986)). Ringwald turned it down because she felt uncomfortable with the content in the script, and did not like the idea of playing a prostitute. She has since stated in several interviews that she regrets turning the role down.
In the dinner scene when Vivian flings the snail across the room, the waiter says, "It happens all the time." Garry Marshall cast the same actor The Princess Diaries years later and gave him the same line.
Brooke Shields auditioned for the part of Vivian, but she was fired by director Garry Marshall. She later said, that she wanted to play a mature role. She considered that it was the biggest mistake of her life.
In the original plans, Vivian was supposed to be addicted to cocaine and part of the deal is was she couldn't do drugs during the week. And at the end of the movie, Vivian was supposed to find Kit had overdosed on drugs while she was with Edward.
In the final scene, Edward "serenades" Vivian with a recording of an aria from La Traviata. The aria has a vocal solo followed by the theme on strings and trumpet. That arrangement was not from the original opera but adapted for the movie.
Sarah Jessica Parker was offered the role of Vivian, but she disliked the part. However, Parker would play a sexy character many years later, Carrie Bradshaw, on the popular TV series Sex and the City (1998).
The trivia items below may give away important plot points.
The movie was initially intended to be a dark drama about prostitution in Los Angeles in the late 1980s/early 1990s. The relationship between Vivian and Edward also harbored controversial themes, including the concept of having Vivian addicted to cocaine; part of the deal was that she had to stay off it for a week. She needed the money to go to Disneyland. Edward eventually throws her out of his car and drives off. The movie was scripted to end with Vivian and her prostitute friend on the bus to Disneyland. These traits, considered by producer Laura Ziskin to be detrimental to the otherwise sympathetic portrayal of her, were removed or incorporated into the character of Vivian's friend, Kit. These "cut scenes" have been found in public view, and some were included on the DVD released on the movie's 15th anniversary. One such scene has Vivian offering Edward, "I could just pop ya good and be on my way", indicating a lack of interest in "pillow talk". In another, she is confronted by drug dealers outside of The Blue Banana, and rescued by Edward and Darryl. One example of a changed plotline was when Edward breaks into the bathroom to find Vivian flossing her teeth instead of doing drugs as he had feared. In the original script she was doing drugs.
You can see Richard Gere moving his tongue around inside his mouth as he is at the door of the penthouse yelling at Stuckey when he fires him and throws him out of the penthouse after catching him molesting Vivian. This is because Gere actually knocked a crown off of a molar during the scene, according to the director's commentary by Garry Marshall on the DVD.