The first use of computer digitized images as part of a feature film (not merely monitor graphics) was the Gunslinger's point of view in Westworld. After the process was finally developed enough to produce satisfactory results, it took a mere eight hours to produce each ten seconds of footage for the Gunslinger's pixelated POV.
Michael Crichton became inspired to write this film after a trip to Disneyland, where he saw the Pirates of the Caribbean ride, and was impressed by the animatronic characters. Furthermore, the ride is mentioned in Jurassic Park (1993), when Malcolm says "When the Pirates of the Caribbean breaks down, the pirates don't eat the tourists.", unlike what happens in this film. Jurassic Park (1993) was based on the novel by Westworld director Michael Crichton.
There were several minor injures during filming. During a shootout scene a piece of wadding from a blank cartridge struck Yul Brynner in the eye, scratching his cornea and leaving him unable to wear his light reflecting contacts without his injured eye turning red and tearing up, so shooting had to be maneuvered to allow time for his eye to heal. And during the scene where James Brolin's character was bitten by a rattlesnake, while the milked rattler was attached to Brolin's arm, he was bitten by the teeth on the snakes lower jaw, despite wearing padding on his arm made of leather and cotton.
Michael Crichton would later use the similar plot line about an amusement park that goes horribly wrong and the attractions malfunctioning for his novel "Jurassic Park", which would become the hit film Jurassic Park (1993) 20 years later.
After the filming of Terminator 3: Rise of the Machines (2003), Arnold Schwarzenegger was to produce and star in a remake of Westworld for Warner Bros. After that, he was meant to star in a sequel to Conan the Barbarian (1982), pairing him with a younger swordsman. Both these plans never came to fruition after Schwarzenegger was elected Governor of California in 2003.
During the 3rd stand-off with the Gunslinger when John decides to take him on, Yul Brynner slips off and tucks the thong of his revolver in exactly the same way his character Chris repeatedly does in The Magnificent Seven (1960)
Michael Crichton re-edited the first cut of the movie because he found it long and boring it was. The deleted scenes include: the bank robbery and sales room sequences, hovercraft with passengers flying above the desert in the beginning, additional and longer dialogue scenes, more scenes with robots going crazy and killing guests (including a scene in which a guest is tied down to a rack and killed when his arms are pulled out), a longer chase scene with Gunslinger chasing Peter, and Gunslinger cleaning his face with water after Peter throws acid on him. Crichton's assembly cut also had a different ending, which included a fight between Gunslinger and Peter (deleted because it seemed staged and foolish), and an alternate death scene in which Gunslinger was killed with the same rack used to kill one of the guests.