The Beast Within is a 1982 American horror film directed by Philippe Mora from a screenplay by Tom Holland. Ronny Cox, Bibi Besch, Paul Clemens, and Don Gordon star in the film. The story centers on a couple's son, who begins exhibiting strange behavior after his 17th birthday.

Producer Harvey Bernhard had purchased the rights to the then-unfinished novel based on the title alone. Due to the book not having been finished prior to production, the resulting script bears little resemblance to the source material. Principal photography officially began on February 8, 1981, in and around Jackson, Mississippi and concluded on April 10, 1981.

The Beast Within was released theatrically on February 12, 1982. It grossed a total of $7.7 million worldwide. The film received negative reviews from critics.