Denzel Washington was cast in this film because of a trip to a doctor. He ran into director Tony Scott in the waiting room of a medical office and the two men started chatting. Scott had not seen Washington in person since they worked together on Crimson Tide (1995). Scott happened to see Dakota Fanning in I Am Sam (2001) the night before and seeing Washington made Scott think using of the two actors together.
Dakota Fanning was missing her front teeth during filming. The film-makers debated whether they should add fake teeth on her and even made them for the actress. In the end, they decided not to use them.
Writer Brian Helgeland first saw the original Man on Fire (1987) when he was renting videos in the late-'80s. He walked in to the video store where Quentin Tarantino was working, and asked what was good. Tarantino recommended Man on Fire (1987).
Creasy's quote about arranging a meeting between the kidnappers and God is similar to a quote falsely attributed to General Norman Schwarzkopf. It is not clear whose work the original quote is, which goes: "It's God's responsibility to judge 'Osama bin Laden'. It is our responsibility to arrange the meeting."
In A.J. Quinnell's novel Dakota Fanning's character in Italy was named Pinta. After director Tony Scott's changed the film's setting to Mexico and discovered that "Pinta" is Mexican slang for "whore", he had the name changed to "Pita" and made her full name Lupita.
Writer Brian Helgeland was not really keen on writing a movie he probably would not end up directing, so the producers told him that Tony Scott was working on another project that he might shoot instead of Man on Fire. In the end, that other project didn't end up getting made, and Scott ended up directing.
When Creasy reads the address of Aurelio Sanchez on the piece of paper, you can see that the street name is 'Via Appia'. This street doesn't actually exist in New-Mexico, but it obviously refers to the ancient Via Appia road in Rome. Heavy criminals used to be crucified by the side of that road, to make a statement towards society and especially towards other criminals.
Interesting name: John Creasey (with the second "e") was a popular and prolific British writer of crime and detective fiction, the original creator of The Baron (1966) and Commander George Gideon of Scotland Yard (filmed more than once, most notably with Jack Hawkins as Gideon in Gideon of Scotland Yard (1958).
The kidnappers first names in the movie, Daniel and his brother Aurelio, are the actual first names of real life Mexico City kidnappers in the late 90s, Daniel and Aurelio Arizmendi Lopez, the infamous "Ear Loppers".