1. The film is based on a poem Tim Burton wrote in 1982 while working as an animator for Disney.
2. Disney considered developing The Nightmare Before Christmas in 1982 as either a short film or 30-minute TV special. The studio eventually shelved it for being "too weird."
Disney decided to produce the movie after the success of Burton's films Beetlejuice and Batman.
Source: Los Angeles Times
3. Jack Skellington first appeared in Beetlejuice (1988). His head can be seen atop Beetlejuice's carnival hat.
4. Burton did NOT direct the movie due to the film's time commitment and his scheduling conflicts with Batman Returns.
5. The film used over 230 sets that were set up in 19 soundstages.
6. The sets were designed to look like the ink illustrations of Ronald Searle and Edward Gorey.
7. It took an entire week of shooting to create one minute of film.
8. Burton’s friend and composer Danny Elfman wrote the songs and music for the film without a script or storyboard.
9. Elfman also provided the singing voice for Jack after it was discovered that Chris Sarandon, Jack's speaking voice, could not sing.
10. In the scenes with the street band, there is a small man inside the bass who is based on Elfman.
11. Elfman also provided the voices for Barrel and the Clown with the Tear-Away Face.
12. Patrick Stewart was the film's original narrator but was cut at the last minute for unclear reasons. He does, however, appear as the narrator on the film's soundtrack.
13. In the original ending, Oogie Boogie was actually supposed to be Doctor Finklestein in disguise.
This was changed before filming.
14. The film was only a modest success at the box office — earning just $50 million during its first theatrical run.
15. Disney wanted to build a Nightmare Before Christmas ride at Disneyland, but reportedly Burton (who owns 50% of the rights to the characters) nixed the idea.
The ride would have been constructed right next to It’s a Small World.
16. Burton also turned down Disney’s request to make a sequel, stating that "some movies should just be left alone. I think it keeps their kind of spirit intact in a way."
17. Jack makes a cameo as a pirate skeleton in James and the Giant Peach.
18. He also makes hidden cameos in several films: as a shadow in the The Princess and the Frog, as a print on the Mad Hatters' bow tie in Alice in Wonderland, and inside of an egg in Coraline.
Bonus: Patrick Stewart reading The Nightmare Before Christmas poem part 1:
Patrick Stewart reading The Nightmare Before Christmas poem part 2:
Facts come via The Making of Tim Burton's The Nightmare Before Christmas, unless otherwise stated.