Director John Hughes wrote the script in only two days, over the July 4th weekend in 1982.

Hughes makes a cameo appearance as Brian’s father at the end of the film.

Brian’s license plate reads EMC 2″ and Andrew’s reads OHIOST. This is to go along with their nerd and jock appearances.

Allison’s dandruff, which she sprinkles to make it snow, was made of Parmesan cheese.

The movie was initially supposed to be the start of a franchise where new movies would check in on the characters.

Director John Hughes actually went to school at Shermer High.

Anthony Michael Hall’s real mother and sister appear as his character’s mother and sister in the beginning of the film.

Simple Minds’ Don’t You (Forget About Me), which was written specifically for the film, was the band’s only number-one hit.

Judd Nelson’s constant off-screen bullying of Molly Ringwald nearly got him fired by John Hughes. Nelson argued that it was to help him stay in character.

Judd Nelson, who was 26 when filming the movie, was the oldest actor out of the five.

The marijuana the kids smoked in the film was actually oregano.

Claire’s BMW was owned by director John Hughes.

Ally Sheedy suggested the film’s epigram, a quote from David Bowie’s Changes.

During the opening, there is graffiti that reads, I don’t like Mondays. This is a reference to 16-year-old Brenda Spencer, who gave that as the explanation for the school shooting she committed in 1979.

Nelson’s ad-libbed dirty joke —A naked blonde walks into a bar, carrying a poodle under one arm and a six-foot salami under the other…—has no punchline.

Claire’s outfit was purchased in its entirety from Chicago’s only Ralph Lauren store

As an end-of-filming gift, Hughes gave each actor a piece of the library’s banister.

This famous tell-all scene was 100% ad-libbed.