In 1982, the animated film The Secret of NIMH was released, directed by Don Bluth. The film adds a mystical element completely absent from the novel, with Nicodemus portrayed as a wise, bearded old wizard with magic powers and an enchanted amulet, rather than an equal of the other rats. The character of Jenner is made a villain who is still present with the rats, rather than having left them before the story begins. The crow Jeremy receives much greater prominence as comic relief in the film than he has in the book. Additionally, the Frisby family name was changed to "Brisby" to avoid trademark infringement with the Frisbee.
In July 2009, Paramount Pictures set Neil Burger to write the script and Cary Granat to produce the film based on the book.
On March 4, 2015, MGM acquired the rights to the book to adapt it into the live-action/animated film, set Michael Berg to adapt it, while Daniel Bobker and Ehren Kruger would produce.