This film is loosely based on the Daniel P. Mannix novel of the same. Almost every aspect from the novel was either changed or eliminated entirely. In the novel, Tod and Copper were never friends and met by Tod mocking his human caretaker's neighbor's hounds on their land; Chief's and Copper's ages were reversed and subsequently their roles of who was jealous of whom were reversed; Tod intentionally kills Chief by jumping out of the way of an oncoming train; Tod had two vixens that he mates and has cubs with, all of whom are killed by the hunter; Tod dies from exhaustion while being chased by Copper; the hunter was an old drunk and the novel ends with the hunter being sent to a retirement home and, because dogs aren't allowed, forced to shoot Copper.
The last Disney animated feature to simply end with a "The End; Walt Disney Productions" credit, as with all previous Disney animated films after Alice in Wonderland (1951). (All of the credits were at the beginning.) The next Disney animated feature, The Black Cauldron (1985), was the first one with closing credits.
Frank Thomas and Ollie Johnston collaborated on a book in 1993 called "Disney Villains" where they revealed that they do not believe that the bear in this film is a villain as it, much like the rat in Lady and the Tramp (1955), was acting purely out of instinct.
Originally, when Chief got hit by the train, he was supposed to die, which was supposed to fully justify Copper's revenge at Tod. However, for the same reason as Trusty from Lady and the Tramp (1955), some of the crew had qualms against eliminating a main character, mostly because of the risk of the scene being too intense for children.
An uncredited Tim Burton did the character animation for the character Vixey. She was so different from the dark and Gothic-loving Burton's style that he initially only animated her with distant shots; the closeup of her was done when Burton "grew to like her."
Animator Glen Keane, who was given the task of animating the climactic battle between Tod and the bear, felt that the storyboards he was given were not dramatic enough, so he re-boarded the whole scene. He also planned to draw the fight in charcoal rather than pencil, but budgetary concerns prevented this.
Contrary to popular belief, Kurt Russell did not record his lines for the film in his costume for Escape from New York (1981); which was released the same year as this film. Escape From New York was filmed in the summer of 1980 and finished and released the following year. This film was being animated in 1980 and voices weren't added until almost six months before its completion and release long after the filming and production of Escape from New York would have ended.
Because of the color of his fur, the Bear is often thought to be an American black bear. However, due to his behavior, size, and visible shoulder hump and claws, it is much more likely that he is a melanistic grizzly bear.
John McIntire and his wife Jeanette Nolan, much like The Rescuers (1977) both voiced characters in the film. McIntire voiced the Grumpy Badger that Tod mets when dropped off in the Forest, whilst Nolan voiced Tod's Human Caretaker Widow Tweed.