Originally proposed by brief Hammer cohort Kenneth Hyman, this movie was planned to be the first in a series of many Sherlock Holmes movies starring Peter Cushing, produced by Hammer Films. When the audiences disapproved of a Hammer movie without any monsters and failed to turn up in great numbers, the planned series was subsequently dropped.
For his role as Sherlock Holmes Peter Cushing had to regularly have a pipe in his mouth. However, Cushing didn't like the taste of the pipe so he kept a glass of milk handy to remove the taste.
André Morell was one of the first movie portrayals to show Watson as a more than competent colleague of Holmes, rather than the lovable buffoon that Nigel Bruce had portrayed.
Sir Christopher Lee readily admitted he had a morbid fear of spiders and the panic on his face during the scene with the tarantula was not due to acting. However, an examination of the scene does not show any shots in which one can see both Lee and a live spider--whenever Lee's face is shown, the spider is motionless--so this may just be publicity hype.
The Baskerville Hall set is a redress of that used for Castle Dracula in Horror of Dracula (1958), in which Sir Christopher Lee and Peter Cushing also starred.