Sir Anthony Hopkins showed up on the set during one of his off days, just so he could watch Philip Seymour Hoffman work. The two actors shared no scenes in the film.

Ralph Fiennes gained fifteen pounds of muscle for the role of Francis Dolarhyde.

Sir Anthony Hopkins stated that one of his goals in playing Hannibal Lecter for a final time was to re-establish that he is an evil serial killer, as Hopkins believed Hannibal had come to be seen too much as a likable anti-hero by audiences.

Ralph Fiennes' back tattoo took eight hours to apply.

Edward Norton says he took every penny from what he made on this film to finance his other film, 25th Hour (2002).

After the film's release, Sir Anthony Hopkins said this would be his last portrayal of Hannibal Lecter.

(At around thirty-four minutes) When Will Graham first encounters Hannibal Lecter in the asylum, it was originally written that Graham would show his fear of Lecter. However, Edward Norton pointed out that Graham was a seasoned, and veteran Agent, who would never show his fear to Lecter. Director Brett Ratner then suggested that Graham would be afraid, but would not show it, and they came up with the idea of Graham having massive armpit sweat stains following his encounter with Lecter.

The Leeds' house previously appeared in Ferris Bueller's Day Off (1986).

(At around twenty-eight minutes) The establishing shot of the Baltimore State Hospital for the Criminally Insane was re-used from The Silence of the Lambs (1991), as the building was no longer available for filming.

Sir Anthony Hopkins, Anthony Heald, and Frankie Faison all reprised their roles from earlier films in the franchise. Faison is the only one to have appeared in the first four Thomas Harris "Hannibal" adaptations, having also appeared in Manhunter (1986) in a different role.

(At around fifty-seven minutes) The painting on Byron Metcalf's wall is a portrait of John Wilkes Booth.

Many lines of Dr. Lecter in the movie are original lines of Dr. Bloom in the book.

Frank Langella recorded lines as the Voice of the Dragon in the scene where the Dragon tells Dollorhyde (Ralph Fiennes) to kill Reba (Emily Watson). Although director Brett Ratner said that Langella did a great job, he felt the voice over didn't work the way he had intended. He then had Fiennes record the lines himself (almost like Dollarhyde's inner voice), but it was finally decided that the scene worked better without a voice over.

Ethan Hawke was the first choice to play Will Graham.

Paul Bettany was offered the role of Francis Dolarhyde but turned it down to appear in Dogville (2003).

Michael Jackson lobbied for the role of Dolarhyde.

When asked to reprise his role in the film, Anthony Heald was unsure if he would be able to. Tim Roth became a candidate for a younger Dr. Chilton, and negotiations began. At the last second, Heald became available. Interestingly enough, Roth was also considered as a possible replacement for Sir Anthony Hopkins in Hannibal (2001), had Hopkins declined.

During filming, Michael Jackson made a surprise visit to the set. He and director Brett Ratner had known each other since Ratner's music video career.

Jack Black was considered for the role of Freddy Lounds.

After finding out that Dolarhyde knows where he lives, Will brings his family to a horse and sheep ranch, a reference to the story of Clarice's childhood in The Silence of the Lambs (1991).

With the exception of the pre-title prologue, all three returning cast members (Sir Anthony Hopkins, Anthony Heald and Frankie Faison) are seen only in the confines of the hospital.

Sean Penn and Nicolas Cage were considered for the role of Dolarhyde.

Screenwriter Ted Tally was unaware that Frankie Faison would reprise his role of Barney, and indicated that he would have elaborated on Faison's role if he had known.

Will Graham appears in only four scenes with Hannibal Lecter in the film, the same number of scenes Clarice Starling shares with Lecter in The Silence of the Lambs (1991).

Costume Designer Betsy Heimann ordered the Dolarhyde clothing from mail-order catalogues, to reflect the character's loner personality, as though he would order clothes this way, in order to avoid human contact as much as possible.

In William Blake's "Great Red Dragon" series of paintings, there are two with very similar names. The novel "Red Dragon," by Thomas Harris, uses the title of one painting ("The Great Red Dragon and the Woman Clothed with the Sun"), but in describing the image, gives a description of another ("The Great Red Dragon and the Woman Clothed in the Sun"). Due to the muddled reference, the first adaptation of the novel, Manhunter (1986), Francis Dolarhyde is obsessed with the painting that Harris cites by name, while this film features the painting as described by Harris, which is a back view of the dragon with his tail wrapped around the woman.

Edward Norton (Will Graham in Red Dragon (2002)) and Jodie Foster (Clarice Starling in The Silence of the Lambs (1991)) both played intellectually gifted FBI agents in the franchise. In real life, they both graduated from the Ivy League's Yale University.

Edward Norton's hair was slightly bleached, as his character lives in a sunny climate, which would make his hair lighter in color.

The B.T.K. (Bind, Torture, Kill) Killer, on whom the Dolarhyde character is based, was captured in 2005, which was three years after the release of this film.

In the Italian version of the film, Harvey Keitel (Jack Crawford) was voiced by Ennio Coltorti, who played Commissioner Ricci in Hannibal (2001).

During shooting of the opening classical concert scene, one of the extras in the audience was conducting along with the actual conductor, requiring a retake.

Director of Photography Dante Spinotti also filmed Manhunter (1986), which was the first adaptation of the novel "Red Dragon." Brett Ratner, who had previously worked with Spinotti on The Family Man (2000), wanted him to shoot this movie so much that he delayed principal photography, just so that Spinotti could finish shooting Pinocchio (2002).

Director Brett Ratner's first choice for the role of Reba was Téa Leoni.

Michael Bay was offered the chance to direct to the film.

Harvey Keitel's role was previously played by Scott Glenn in The Silence of the Lambs (1991). Keitel and Glenn appeared together in Puerto Vallarta Squeeze (2004). They are also both former U.S. Marines.

The film cast includes three Oscar winners, Sir Anthony Hopkins, Philip Seymour Hoffman and Ellen Burstyn (the latter has an uncredited role), and five Oscar nominees, Edward Norton, Ralph Fiennes, Emily Watson, Lalo Schifrin and Harvey Keitel.

Edward Norton, Ralph Fiennes and Harvey Keitel appeared in The Grand Budapest Hotel (2014).

Jeremy Piven auditioned for the role of Dolarhyde.

Harvey Keitel played a character originally played by Dennis Farina in Manhunter (1986). In Get Shorty (1995), Keitel played Farina's character during the "movie within a movie."

Many actors from this film had also worked with the original Hannibal Lecter (Lecktor), Brian Cox. Sir Anthony Hopkins and Mary-Louise Parker appeared with Cox in RED 2 (2013), Edward Norton and Philip Seymour Hoffman in 25th Hour (2002), Emily Watson in The Boxer (1997) and The Water Horse (2007), and Ralph Fiennes in Coriolanus (2011).

Director Brett Ratner originally wanted Michael Mann, the director of Manhunter (1986), to do a cameo as a taxi driver in this film.

Brett Ratner directed Rush Hour 2 (2001) previous to directing this film. In Rush Hour 2 (2001), the main villain's yacht and new casino in Las Vegas are named "The Red Dragon."

Jewish cast and crew members celebrated Passover during the filming of external shots of the climactic scenes at the Dolarhyde house.

The novel "Red Dragon" by Thomas Harris was published in 1981, ten years before Sir Anthony Hopkins was cast as Hannibal Lecter in The Silence of the Lambs (1991). Nevertheless, it would seem that Welshman Hopkins was destined to play Lecter, as the emblem on the flag of Wales is of a large red dragon on a green and white field. In the Welsh language, the flag's name is "Y Ddraig Goch," meaning literally "The Red Dragon."

(At around one hour and four minutes) At the end of Hannibal Lecter's note in the Tattler to the Tooth Fairy, it says "Bless you, 666." 666 is the mark of the Beast in the Book of the Revelation.

Edward Norton worked with Scott Glenn, the previous actor of Jack Crawford, in The Bourne Legacy (2012). Harvey Keitel worked with Jodie Foster (Clarice Starling) in Taxi Driver (1976).

Emily Watson's role was previously played by Joan Allen. Allen played the wife of Daniel Day-Lewis' character in The Crucible (1996), while Watson played his wife in The Boxer (1997), opposite the original Hannibal, Brian Cox. Edward Norton appeared with Allen in The Bourne Legacy (2012), while Sir Anthony Hopkins appeared with her in Nixon (1995).

Red Dragon is also the name of a rumored book in the Vatican Library said to be able to summon the Devil and thus it gives the Pope some of his Authority.

The orchestral work performed at the beginning is the Scherzo movement from A Midsummer Night's Dream by Felix Mendelssohn. It is part of the standard flute audition repertoire for almost every orchestra around the world, so a flutist is expected to perform it flawlessly.

Hannibal (2001) was directed by Ridley Scott. Harvey Keitel appeared in Scott's first film, The Duellists (1977), and subsequently in Thelma & Louise (1991).

Mary-Louise Parker and Anthony Heald appeared in The Client (1994).

Frankie Faison and Al Brown, who played Barney Matthews and the Tattler Guard respectively, both appeared on The Wire (2002). They were both high ranking police officers: Faison played Ervin Burrell, while Brown played Stanislaus Valcheck.

Two Jack Crawfords (Scott Glenn in The Silence of the Lambs (1991) and Harvey Keitel in this film) were cast in Apocalypse Now (1979): Glenn as Colby and Keitel as Willard (famously replaced by Martin Sheen). Laurence Fishburne (Jack Crawford from the television series Hannibal (2013)) also appeared in Apocalypse Now (1979), as Tyrone Miller.

In the book Red Dragon by Thomas Harris, Will Graham's son is named Wally. In the film Manhunter (1986) Will Graham's son is named Kevin. In this film his name is Josh.

Edward Norton and Ken Leung appeared in Keeping the Faith (2000).

Philip Seymour Hoffman insisted on actually being glued to the chair during his encounter with Dolarhyde.

During the scene where Will Graham (Edward Norton) realizes that Hannibal Lecter (Sir Anthony Hopkins) is the killer he is looking for, Lecter stabs him with a knife, but Graham fends him off with an arrowhead. This may be a subtle reference to how Hannibal was exposed in the novel. One of his victims was found horribly mutilated with multiple stab wounds. Graham discovers that the victim has a scar from an old wound that was caused by an arrow, and finds out that Hannibal Lecter was the physician who had treated the wound. Graham visits Lecter a few times in the hope that Lecter may be able to provide a helpful lead. During one visit, he notices an illustration in one of Lecter's books, depicting a man with the exact same stab wounds as the victim, which makes him realize that Lecter is the killer. However, just as in the movie, Lecter surprises Graham and nearly stabs him to death.

The musician that Hannibal sees playing badly, and later serves to his dinner guests, was meant to be Benjamin Raspail, whose head Clarice Starling finds in The Silence of the Lambs (1991). In that film, Hannibal tells Clarice that he did not kill Raspail, merely "tucked him away, much as I found him." This is not a discrepancy in the book. Hannibal admits to having killed Raspail. The head in the jar was another man named Klaus.

The death of Freddy Lounds (Philip Seymour Hoffman) was filmed by setting a real stunt man (wrapped in protective material) on fire as his wheelchair rolled down the street. No puppets or animatronics were involved.