Universal Pictures saw this movie as a risk and would only put up an $18 million budget, not enough to pay the two main stars and the director their normal fees. They decided to agree to 40% of the gross profits split between the three of them, and ended up making more than they would have made taking their fees upfront, as the film was a huge hit that took in $216 million worldwide.
Because the studio was reluctant to let Arnold Schwarzenegger try comedy, he agreed to waive any upfront salary, and took 20% of the prospective profits instead. He made over $40,000,000 from domestic and international sales, video/DVD sales and TV screenings, earning more money from Jumeaux (1988) than any of the Terminator movies.
Arnold Schwarzenegger had always wanted to do a sequel called Triplets, with Danny DeVito returning and adding Eddie Murphy as a long lost third brother. DeVito pitched script ideas back in 2003 but Schwarzenegger was too busy running for governor of California. DeVito agreed with his decision but doubted he would become governor. In 2012, at the end of Governor Schwarzenegger's second term, plans for the sequel were officially confirmed, but in 2019, DeVito publicly disclosed that although Triplets was in pre-production, the final script was still incomplete. Ivan Reitman confirmed during press of SOS fantômes: L'au-delà (2021) that he would return as director, as would Schwarzenegger and DeVito in their original roles, but the role of the third brother would now go to Tracy Morgan (whom had just worked with Murphy on another long-in-development sequel, Un prince à New York 2 (2021)); production was to start in 2022. These plans were all canceled after Ivan died early 2022, and his son Jason Reitman (director of Ghostbusters Afterlife) confirmed that he would not take over.
Arnold Schwarzenegger decided to do the film because he thought he'd be great in a comedy and wanted to go beyond making action movies. In 2016, he went on record as stating that investing in himself by trying comedy and forgoing his salary in exchange for a share of the film's profits was the best decision he ever made.
In an interview with the Academy of American Television, Danny DeVito said when he was called to make the film, he asked if the other twin had been hired. As soon as he found out it was Arnold Schwarzenegger, he asked: "The Austrian bodybuilder?" When he was confirmed, Danny said: "I am signing. Nobody will believe I am the twin brother to Arnold Schwarzenegger."
Cary-Hiroyuki Tagawa: at the beginning of the movie as Julius's martial arts instructor. In the end credits, he is credited as "Oriental Man".
Catherine Reitman: (the director's daughter). She would later portray the recurring character of Maureen Ponderosa on It's Always Sunny in Philadelphia (2005) which stars Danny DeVito.