Don Bluth, John Pomeroy and Gary Goldman all left Disney to pursue this project, which had originally been rejected by their former employer as "too dark" to be a commercial success. They were followed soon after by twenty other Walt Disney Productions animators, dubbed "The Disney Defectors" by the trade press.
At the time of release, it was the largest non-Disney animated movie.
The lead character's name was changed from Mrs. Frisby (in the novel) to Mrs. Brisby to avoid legal entanglements from the Wham-O company (makers of the Frisbee). Unfortunately, this change came late in the movie's production, long after the actors and actresses had recorded their dialogue. Because it was not feasible to have every actor and actress using the word "Frisby" in the movie re-record his or her lines, the change from "Frisby" to "Brisby" was actually made by the sound editors, who, by hand, carefully sliced the "br" (taken from other words spoken by the actors and actresses) into the "fr" on the magnetic dialogue tracks.
The small dragonfly Mr. Ages chases away near the beginning of the movie is a nod to Evinrude from Disney's Bernard und Bianca - Die Mäusepolizei (1977), one of the last movies Don Bluth worked on at Disney before leaving the company.
This was Jerry Goldsmith's first music score for an animated movie. He later said that it was among his personal favorites. He was instrumental in introducing the movie to Steven Spielberg, who went on to work with Don Bluth on Feivel, der Mauswanderer (1986). According to Bluth and Gary Goldman in their DVD commentary, Goldsmith so loved the movie that he volunteered an extra three weeks to polish and refine the score, even though he was not contractually obligated to do so.