Isle of Forgotten Sins is an American South Seas adventure film released on August 15, 1943 by PRC, with Leon Fromkess in charge of production, directed by Edgar G. Ulmer (also credited with original story) and featuring top-billed John Carradine and Gale Sondergaard whose performance in one of 1936's Academy Award for Best Picture nominees, Anthony Adverse, earned her the first Academy Award for Best Supporting Actress.

Isle of Forgotten Sins was subsequently reissued in a version cut from 82 to 74 minutes and retitled Monsoon. It proved to be the final film role for German-American actress Betty Amann as well as the last feature for producer Peter R. Van Duinen's Atlantis Pictures, a unit whose films had a higher budget then most of PRC's releases. Third-listed supporting actor Sidney Toler worked on this PRC title between the finish of his Charlie Chan films at 20th Century Fox and just before their resumption at Monogram Pictures. The film features several songs (with Carradine singing "Whiskey Johnny"), an underwater sequence using a marionette and a tropical monsoon climax. The pre-release working title was Island of Forgotten Sins.