1. Twins Hallie and Annie, played by Lindsay Lohan, are named after director Nancy Meyers and producer Charles Shyer's real-life daughters.
2. The film says "For Hallie" in its final credits. This is a dedication to Meyers and Shyer's daughter of the same name.
3. The real Hallie and Annie had cameo roles in the film. Annie plays the towel girl who brings Elizabeth the first-aid kit at the hotel, while Hallie plays the girl at Camp Walden who asks where the Navajo bunk is.
4. Camp Walden is based on an existing camp for girls in Denmark, Maine.
5. Joanna Barnes plays the wicked girlfriend in the original 1961 The Parent Trap. She plays the wicked girlfriend's mother in the 1998 version. Both characters are called Vicky.
6. Erin Mackey, Lohan's acting double, is seven years older than her.
7. Mackey now works in musical theatre, and played Glinda in the Chicago, Los Angeles, and Broadway productions of Wicked.
8. A scene in which Hallie meets the Queen in London was cut from the final version of the film.
9. One of the main camp counselors, Marva Kulp Jr, is Janice from Friends.
10. Marva Kulp Sr and Marva Kulp Jr are named after Nancy Kulp, who played one of the camp counselors in the original The Parent Trap.
11. The music that plays when Hallie and Martin do the secret handshake is the intro to "Am I the Same Girl" by Dusty Springfield, which includes the lyrics: "Why don't you stop and look me over? / Am I the same girl you used to know?"
12. The secret handshake consists of 18 moves.
13. It took Lohan an hour to learn.
14. Michelle Trachtenberg was considered for the role of the twins. Her birthday is 11 October, the same as Hallie and Annie's in the film.
15. Scarlett Johansson also auditioned for the roles of Hallie and Annie.
16. So did Mara Wilson.
17. When Hallie arrives in London, Elizabeth takes her to a photo shoot. In this scene, The Beatles' "Here Comes the Sun", from their Abbey Road album, plays. Hallie and Elizabeth cross the same street in the same way as The Beatles did for the album cover shoot. Even the cars on the side are positioned identically.
18. The Parent Trap was Lohan's first movie.
19. She had her ears pierced especially for the role.
20. In the UK, the ear-piercing scene was cut so as not to encourage underage piercing.
21. When Lohan wasn't needed for a scene, the director let her call "action".
22. When Nick sees Elizabeth for the first time in 11 years, his reaction – leaning out of the lift and almost falling over – is identical to Cary Grant's reaction to seeing the wife he believes dead in My Favourite Wife (1940).
23. Meredith talks to Reverend Mosby on her phone. This is a reference to a character in the original The Parent Trap.
24. The opening and ending sequences feature love songs performed by Nat King Cole and his daughter Natalie Cole respectively. In the opening scene, "L-O-V-E" plays over images of Nick and Elizabeth's first wedding. In the ending sequence, "This Will Be (an Everlasting Love)" plays over photographs of Elizabeth and Nick's second wedding.
25. The Stafford, where Nick and Elizabeth are reunited, is named after a boy in the original The Parent Trap. Stafford is the boy Susan talks to at the camp dance when Sharon cuts off the back of her dress.
26. Lohan's mother, Dina, and siblings, Dakota, Michael, and Ali, are extras in the scene where Hallie arrives in London and greets Martin at the airport.
27. The music that plays when the girls walk to the isolation cabin was originally used in The Great Escape.
28. As Hallie meets Meredith coming out of a lift in the hotel, she is mumbling "Let's Get Together", which was a song from the original movie.
29. The word "actually" is uttered 23 times in the film.