Although they had both appeared in Hamlet (1948), Moulin Rouge (1952), and Alexander der Große (1956), Christopher Lee and Peter Cushing met on the set of the film for the first time. They would pass the time between shots by exchanging "Looney Tunes" phrases and quickly developed a fast friendship, which lasted until Cushing's death in 1994.
Christopher Lee and Peter Cushing's friendship was sparked when Lee stormed into Cushing's dressing room, complaining that "I've got no lines!" Cushing kindly responded, "You're lucky. I've read the script."
The script called for a child actress to play Hazel Court's character, Elizabeth, as a little girl of three or four in flashback scenes. Court suggested to the producers that her daughter, Sally Walsh, who looked very much like her mother, play the part. As Court said in an interview, "She hated it - HATED being in it! I think it was all foreign to her, and she didn't understand it. She still remembers it to this day, and still doesn't like it!"
Melvyn Hayes explains in the Blu-ray making of featurette how producer Peter Rogers told him about the casting process of the monster. According to Rogers, a memo went out indicating Hammer was looking for someone big to play the monster. In the end, it boiled down to Sir Christopher Lee and Bernard Bresslaw. Both of their agents were phoned, asking them how much money they wanted. Bresslaw's minimum fee was ten pounds a day, whereas Lee's was eight. "And so, for the sake of two pounds, Christopher Lee became an international star", according to Hayes.
Many film historians credit this movie's success with resurrecting the horror genre, which had very much declined in popularity from its heyday of the 1930s and early 1940s.