Author Existence Failure: Poor, poor Mary Wickes, Laverne's voice actress. This was her final film role as she died of cancer during production and had to be replaced by a stand in, although thankfully only for a few lines. Fortunately, that stand-in is sound-alike Jane Withers, who took over the role in much-maligned DTV sequel.
Reversed in Sweden, in the dub the same guy voices Ratcliffe and Frollo.
Mean Character Nice Actor: In an interview for Disney Adventures that was published right around the time that the movie was released, Tony Jay made it a point to say that he was actually a very nice man in Real Life, despite continually playing villainous roles (and with Frollo being one of his darker ones).
Non-Singing Voice : Averted; with the exception of Esmeralda, every actor does their own singing. Tom Hulce, Quasimodo's voice actor, wanted to be a singer when he was younger.
Talking to Himself: During the flashback in the opening number, Jim Cummings voices about three or four characters in quick succession (one or two of the gypsy men, the boatman, and Frollo's guard). While Cummings does have an impressive vocal range, he unfortunately uses the same voice for all of these characters, making it very noticeable.
Technology Marches On: When the film was being promoted, the CGI people were touted as a huge technological advancement. They were the logical next step after the CGI stampede scene from The Lion King. Instead of using CGI to reproduce the same model making the same movements over and over again, the crowds of Hunchback were randomized, with different elements such as clothing, body types, and behaviors being mixed and matched to create these gigantic Ben Hur crowd scenes that would, otherwise, either be much too expensive to animate, or have to be static parts of the matte. It's more noticeable now (especially if you remember watching "Behind the Scenes" featurettes which showcased the various behaviors back on the '90s Disney Channel), but at the time, especially on a first-time viewing, they were pretty impressive and evocative towards the party atmosphere in "Topsy Turvy" especially.
Throw It In: Phoebus's actor named his horse "Achilles" for the sake of the "Achilles, heel" joke.
What Could Have Been: Phoebus's speech rallying citizens to rebel against Frollo during the climax of the movie was originally said by Clopin, but the directors/producers felt that Phoebus needed to be more involved in the uprising.
Instead of Victor, Hugo and Laverne the gargoyles would have been named Chaney, Laughton and Quinn as homage to actors Lon Chaney Senior, Charles Laughton and Anthony Quinn who had played the title character in previous adaptations.
Fake Nationality: In the 1939 version, the French characters are played by British and American actors. In the 1956 version, most actors are French, but Esmeralda is played by the Italian Gina Lollobrigida and Quasimodo by the Mexican American Anthony Quinn.