The script was rumored to have been dumped on the doorstep of Keanu Reeves' house, a tactic that piqued his interest, and led to him accepting the role of Johnny.
According to William Gibson, the movie was re-edited by the producers in order to make it more "mainstream". The Japanese release is said to be closer to the director's and Gibson's original vision.
At one point, Johnny's brain implant is detected by a security scanner and is falsely reported as a device for counteracting dyslexia. Keanu Reeves does in fact suffer from the disorder in real life.
Robert Longo and William Gibson originally intended to make an art film on a small budget, but failed to get financing. Longo commented that the project "started out as an arty $1.5 million movie, and it became a $30 million movie, because we couldn't get a million and a half."
During the scene in the back room of Crazy Bob's Computer Store, it sounds like Johnny asks for an "iPhone", twelve years before it was launched. While it would still be cute if the scriptwriter of a 90's cyberpunk movie had just made up a word, which would later become the name of a ubiquitous piece of information technology, what Johnny asks for is actually an "Eyephone", an early head-mounted interface designed by Jaron Lanier (in fact, Johnny calls it a "Thomson Eyephone", a reference to the fact that Lanier's patent was bought by Thomson Electronics).