When this film was originally released its title was "The Great Mouse Detective." When Disney re-released it years later they gave it the title of "The Adventures of the Great Mouse Detective." When the film was released on video a few months later, the title on the box was back to "The Great Mouse Detective" but the title on the film itself read "The Adventures of the Great Mouse Detective."
Sherlock Holmes speaks with the voice of Basil Rathbone. Although it is often erroneously claimed that the lines are taken from one of Rathbone's 1940s performances as Sherlock Holmes on film or radio, this is not true. The cameo is edited from Rathbone's reading of the Sherlock Holmes story "The Adventure of the Red-Headed League" by Arthur Conan Doyle for Caedmon Records in 1966, just months before his death. This explains why Rathbone's voice sounds older and less crisp than in his famous films, and more importantly, why the voice of Rathbone's co-star Nigel Bruce was not used for Dr. Watson's brief cameo. According to the text of "The Adventure of the Red-Headed League", this would mean that the film takes place sometime in the autumn of 1890.
The clock tower scene is the first major use of computer animation (the clock's gears) in a feature-length animated film. The same scene was also the first time traditionally-animated characters were put inside a computer-generated background.
Basil of Baker Street is named after Basil Rathbone, who played Sherlock Holmes in 14 films. By strange coincidence, Basil was also a name used by a disguised Holmes in Arthur Conan Doyle's "The Adventure of Black Peter."
Alan Young had performed a near-perfect Scottish accent as the voice Scrooge McDuck for the 1977 Disneyland Records adaptation of "A Christmas Carol" (which he also developed and wrote). He repeated the role of McDuck in Mickey's Christmas Carol, and was a natural for the Scotish brogue of Hiram Flaversham.
When designing Fidget, the Disney animators were focused on creating a scary, yet comical and lovable character. They were looking for a raspy voice and chose Candy Candido, who had starred in voice-over roles in many previous Disney films as well as Ralph Bakshi films. His own looks were used in matching Fidget's looks. Candido's deep, throaty voice was sped up to avoid Fidget's voice from becoming too low. (Candido's original voice can be heard as the mouse shouting "Get off, you eight-legged bum!" at the juggling octopus in the pub.)
As Ratigan is ranting about how much he hates Basil, we see that he has a voodoo doll in the shape of a mouse in a deerstalker. The doll bears a striking resemblance to Basil, not as he appears in this film, but as he appears in Paul Galdone's illustrations in the book on which the film is based.
CASTLE THUNDER: It is heard every time lightning flashes during the storms in this film, and a version played at slow speed is heard a few times. This was the last animated Disney movie to regularly use the Castle Thunder sound effect. Starting with The Black Cauldron the previous year, Disney began trying out newer, digitally-recorded thunder sounds.
"Let Me Be Good To You" was originally to be sung by Madonna, but the directors decided that this was not contemporary enough for the audience to enjoy. After Liza Minnelli was briefly considered, Melissa Manchester was hired as the new singer of the song. "Let Me Be Good To You" was also once entitled, "Look At Me".
The first meeting between Basil and Dawson where Basil guesses he came from Afganistan and gives a complicated explanation how he assume it, mirrors first meeting between Holmes and Watson in Arthur Conan Doyle's "A Study in Scarlet" (the first Holmes novel) where Holmes does the same thing.
The trivia items below may give away important plot points.
As Basil was based on Arthur Conan Doyle's Sherlock Holmes, Rattigan was based on Holmes' arch-nemesis Moriarty, and, like Moriarty, Rattigan fell to his death with Basil (Holmes) while Basil escaped death.