The money was not available to pay to the two main stars and the director their normal fees. They decided to split a percentage of the gross profits between the three of them and ended up making more than they would have made taking their fees upfront because the film was such a hit.
Schwarzenegger got 20% of the profits, and made $35,000,000 through international sales, video/DVD sales and TV screenings. He earned more money from I gemelli (1988) than any of the Terminator movies.
Universal needed to know if Arnold Schwarzenegger, Danny DeVito and Ivan Reitman were committed very early on because they were under deadline. They made the deal on a napkin at lunch with agents; they signed it and DeVito then had it framed.
Arnold Schwarzenegger has always wanted to do a sequel, called Triplets with Danny DeVito 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, although as of 2019, Triplets is still in pre-production, and in April 2019, DeVito publicly disclosed that the final script is still incomplete. Ivan Reitman confirmed during press of Ghostbusters: Legacy (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, Il principe cerca figlio (2021)).
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 C'è sempre il sole a Philadelphia (2005) which stars Danny DeVito.