• Trivia

• The trailer shows part of a scene that is not included in the theatrical release, in which Damien helps Cady booby trap a table in the school cafeteria in an attempt to make Regina spill food all over herself. Of course, it's Karen who sits at the table and inadvertently becomes the victim of the prank. This is shown in its entirety as one of the DVD's deleted scenes.
• Nearly earned an R rating for explicit, risqué gags and jokes which were subsequently cut.
• In the book upon which the movie is based, the most popular girl in a school is given the title "Queen Bee". In the movie, the character who fits that description is named Regina - "queen" in Latin.
• The goth girl Janis Ian was named after the singer of the same name, who wrote the song "At Seventeen" which can be heard playing in the background when the girls were fighting at Regina's house.
• Amy Poehler who plays Mrs. George is only five years older than her on screen daughter Rachel McAdams (Regina George).
• Although the movie was not filmed in the rich north suburbs of Chicago known as the 'North Shore' (where it is said to take place), several real places in the area are mentioned. These include Old Orchard Mall in Skokie, Il (although the scene was filmed at Sherway Gardens in Etobicoke,ON ),Walker Brothers Pancake House (the gift certificates at the end have the restaurant's real logo), and Northwestern University. In addition, a deleted scene featured on the DVD mentions Hecky's, a real barbecue restaurant in Evanston, IL. School scenes were filmed at Licoln Park High School, Chicago. Exterior shots of the school were of Etobicoke Collegiate Institute, Etobicoke, as well as hallway scenes. Some scenes also filmed at a lake front park in Lincoln Park, Chicago.
• Kevin Gnapoor's phone number on his business card uses the North Shore's real area code, 847.
• Tim Meadows makes a reference to a "Saturday Night Live" (1975) character he created. During the gymnasium confessional, he begins the talk by asking, "Is there anyone here with a lady problem?" - the catchphrase of talk show host Leon Phelps, aka "The Ladies Man".
• Amanda Seyfried, who plays Karen in the film, was almost cast as Regina, but producer Lorne Michaels thought she may be better as the "dumb girl".
• Tim Meadows broke his hand before shooting and had to wear a cast, so the explanation that his character Mr. Duvall had carpal tunnel was added.
• Lacey Chabert was the first and only choice for the role of Gretchen.
• Rachel McAdams was told to partly model the character of Regina George after Alec Baldwin's performance in Glengarry Glen Ross (1992).
• In the scene where Cady was asked if her "muffin was buttered", the line was originally going to be, "Is your cherry popped?" The same goes for the girl who "made out with a hot dog" this was going to be "masturbated with a hot dog". These were omitted in order for the film to gain a PG 13+ rating instead of a R
• This movie is based upon the book "Queen Bees and Wannabes: Helping Your Daughter Survive Cliques, Gossip, Boyfriends, and Other Realities of Adolescence" by Rosalind Wiseman, even though it is a non-fiction parental self-help guide with no narrative at all.
• In the scene where Christmas candy canes are being distributed in the classroom Damien, dressed in a Santa suit, reads out the name "Glenn Cocco". Glenn Cocco is a good friend of Tina Fey.
• The song played while Janis and Damien are explaining the cafeteria setting is Fatboy Slim's remix of Pierre Henry's "Psyche Rock". It also served to inspire (and sounds similar) to the theme song of the television show "Futurama" (1999).
• Tina Fey and Amy Poehler coached Rajiv Surendra on how to rap for his on-screen performance in the school's Winter Talent Show.
• Cady's mom gets tenure at Northwestern, which is Ana Gasteyer's alma mater in real life.
• Producer Tina Fey confessed that, when casting the film, she liked Jonathan Bennett (Aaron Samuels) because "he looked like Jimmy Fallon".
• The skirts for the Christmas talent show are made of plastic; the costume designer says they were made of that fabric to "represent the Plastics".
• Initially, Lindsay Lohan was cast as Regina, and Amanda Seyfried was supposed to play Cady.
• The character Mrs. Norbury was named after a French teacher at Upper Darby High School, where Tina Fey attended.
• The scene in which Cady walks in on Jason and Gretchen kissing at her party is much different in the first draft of the script. Originally, she walks in on Gretchen performing oral sex on Jason (no nudity, nothing graphic), but this was subsequently cut from the final print in order to achieve a PG-13 rating
• The teacher talking German in the beginning of the movie speaks French in the German dubbed version.