Artist John Bolton painted the picture of the Shadmock used in the film before the role was even cast. He was genuinely amazed when the film's producers found an actor, James Laurenson, who actually physically resembled the image in the picture.
This is the only film, in a long career of horror and other roles, where Vincent Price played a vampire.
Milton Subotsky claimed he originally planned for the film to include all six of the six top horror film stars at that time in major roles in it - that is, Vincent Price, Peter Cushing, Christopher Lee, Klaus Kinski, Donald Pleasence, and John Carradine. Cushing, Lee and Kinski all turned it down, but Price, Pleasence and Carradine all appeared in the film.
Tie-in merchandise for this film is very rare and highly sought after by its fans. Dez Skinn, John Bolton and David Lloyd produced a graphic novel adaptation of it which was given away at the Cannes Film Festival. Only 1,000 copies were printed. The film's soundtrack on LP record, which was released by Chips Records, is seldom seen and tends to sell in the triple digits when it does turn up. A paperback edition of the film's source novel by R. Chetwynd-Hayes containing artwork that was featured in it was published in 1981 and reprinted in 2013.