Richard Matheson's book was written as a series of flashbacks so that you got into the cellar with Scott quickly. Universal insisted on a linear story. They also vetoed key sequences, such as Scott spending the night with the female midget, a drunk homosexual who abuses Scott, a gang of teenagers who terrorize him, and Scott becoming a Peeping Tom secretly spying on a teenage baby-sitter. These were rejected as too risqué for 1957.
The special effects technicians were able to create giant drops of water by filling up condoms and dropping them. According to Jack Arnold about 100 gross of them were ordered. He said, "I put them on a treadmill and let them drop until the water pipe was supposed to burst, and it was very effective. At the end of the picture, I was called to the production office. They were going over all my expenses and they came across this item of 100 gross of condoms, so they asked me, "What the hell is that for?" I simply said, "Well, it was a very tough picture, so I gave a cast party." And that was all I told them."
Richard Matheson had originally written a screenplay for the sequel called "The Fantastic Shrinking Girl" in which Louise Carey begins to shrink herself. Universal had planned to produce it but the project was eventually scrapped.
Orson Welles did the narration for the film's trailer. He was at Universal working on Touch of Evil (1958).