Norton Juster, author of the book upon which this film is based, had no input on the adaptation, and many characters from the book weren't included in the film. He didn't like the film, and was angered by positive reviews.
This is MGM's first full-length animated film, and the last film the studio released with live action and animation. MGM's animation studio closed soon after this film's release.
This film was made in 1967-68, but it wasn't heavily promoted due to MGM's financial problems and frequent management changes. When it was finally released in 1970, the studio only showed it for 2 weeks, as a weekend matinee. It was not a box-office success.
The final animated film to be made for MGM before Warner Bros. exclusively owns the animated movies from MGM's pre-1986 library from Ted Turner.
Butch Patrick was 13 years old in 1967, when the live-action sequences and voice recordings were done. He was 17 when the film was released in November 1970.