While the film is set in the Caribbean, all of the exterior shots were filmed on and near the island of Ischia in Italy. Historically, the island of Ischia was a pirate haven in the 18th century, making it a suitable location for a period piece. Interior sets were built and filmed at Teddington Studios outside London, England.
The original screenplay by Waldo Salt was rejected by the producers, fearing Salt's Communist ties. Christopher Lee, in his autobiography, claims that director Robert Siodmak changed the original screenplay: