The studios had long wanted to make a sequel to the previous Terminator films, but for a long time Arnold Schwarzenegger refused to do it unless James Cameron was directing. Cameron eventually told his friend to "just do it and ask for a shit-load of money," reasoning that the character was as much Schwarzenegger's as it was his. Schwarzenegger confirmed this in a talk-show interview, saying that when he asked, Cameron told him to "take the money and run".
Edward Furlong was originally supposed to reprise his role as John Connor. However, in December 2001, it was reported that he had been dropped from the film, allegedly due to a substance abuse problem. He was replaced by Nick Stahl shortly before filming began in April 2002. He later said, "It's the growing pains of me. I was part of the project and had a very nice deal but then I guess to celebrate I went out and overdosed on coke and kind of destroyed that whole thing. But I learned my lesson and I'm back on track."
(at around 42 mins) The gas station at which the Terminator stops for refueling is the same gas station seen in all three Terminator movies. In The Terminator (1984) it was shown at the end where the pregnant Sarah stops before driving to the Mojave Desert. In Terminator 2: Judgment Day (1991) it is where Sarah camps in for the night after she escapes from the hospital.
Stan Winston and his team constructed flawless, life-size, fully-operational robotic replicas of Arnold Schwarzenegger and co-star Kristanna Loken because certain sequences involving fire and explosions were too dangerous for them to perform.
Arnold Schwarzenegger worked out for six months, about three hours a day, before shooting started, by which time he said he had the exact same body weight and muscle measurements as he had 12 years previously while shooting Terminator 2: Judgment Day (1991).