Working title: "Gemini". The studio didn't like it, and so switched to "Twins". This was changed to "Dead Ringers" after Ivan Reitman, who had produced two of Cronenberg's early films, approached Cronenberg about purchasing the rights to use the title "Twins". Twins was then used for the Danny DeVito/Arnold Schwarzenegger film Twins (1988).
Initially, Jeremy Irons had two separate dressing rooms and two separate wardrobes which he would use depending on which character he was playing at the time. Soon he realized that "the whole point of the story is you should sometimes be confused as to which is which," after which he moved to a single dressing room and mixed the wardrobes together, and found an "internal way" to play each character differently, using the Alexander technique to give them "different energy points," which gave them slightly different appearances.
William Hurt was Cronenberg's first choice to play the twins. He regretted turning it down but had a scheduling conflict. He later commented about turning down the roles by saying that he "had a hard enough time playing one character, let alone two".
The trailer was cut by 2 seconds in the UK to secure an 18 certificate - trailers are certified more harshly due to their unbidden nature and lack of context. A close-up of Claire's hand being tied to the bed was removed.
The trivia item below may give away important plot points.
The movie is based on two real life twins, Stewart and Cyril Marcus. The two were found dead in their apartment on the Upper East Side of Manhattan. Their deaths were due to withdrawal from barbiturate addiction. The story is told in the novel "Twins" by Bari Wood and Jack Geasland (published 1977).