Monstrosity is a 1963 American science fiction horror film produced by Jack Pollexfen and Dean Dillman Jr. and directed by Joseph V. Mascelli. The film stars Marjorie Eaton, Frank Gerstle, Erika Peters, and Xerxes the cat. It tells the story of a wealthy elderly woman who wants to have her brain transplanted into the head of a young woman. Actor Bradford Dillman, the younger brother of co-writer and producer Dean Dillman, Jr., narrated the film.

Monstrosity was broadcast on television under the title The Atomic Brain.