- Actor Allusion: Bruce Willis gives Slevin the watch that once belonged to Slevin's father. Much like Bruce Willis' character received his father's watch in Pulp Fiction.
- Actor-Inspired Element: Slevin wearing a towel a lot of the time came about because Josh Hartnett lived with writer Jason Smilovic and his wife while the script was being written, and he got so used to seeing Josh in a towel.
- Awesome, Dear Boy: Lucy Liu called this the most fun she ever had on a set.
- Casting Gag: Bruce Willis and Josh Hartnett had both just appeared in Sin City (although they shared no scenes) - where the latter was the reserved hitman.
- Completely Different Title: The play of words on "Lucky Number Slevin" doesn't translate well to a lot of languages so foreign markets had to get creative. Titles used include "The 7 Affair" (in Spain), "Hitman for Hire" (In Mexico) and "Check-Mate" (In Brazil), the latter playing up the film's chess motifs.
- Dawson Casting: Lindsey is meant to be the same age as Slevin, but Lucy Liu is a full ten years older than Josh Hartnett.
- Enforced Method Acting: Theres a scene where Lucy Liu accidentally stumbles in and sees Josh Hartnett completely naked as he adjusts the towel he's wearing. In the original script, that bit wasn't supposed to happen, but as a practical joke Josh took off the towel just as Lucy walked in, flashing her. Lucy's giggle and quiet "sorry" were genuine before she continued delivering her lines.
- Fake American: Sir Ben Kingsley (British) as The Rabbi.
- Insert Cameo: Paul McGuigan's hand is the x-ray in the coroner's office.
- Playing Against Type:
- Typecasting: The second film where Ben Kingsley has suffocated with a plastic bag over his head (after The House Of Sand And Fog) and been knocked unconscious and tied to a chair as part of a revenge scheme (after Death and the Maiden).
- What Could Have Been: An alternate ending was filmed where Slevin killed Lindsey too but that was considered too dark.
Trivia / Lucky Number Slevin