Films:
* Silent Era: There were several silent film adaptations, starting in 1914.
* Sound Era: There are numerous sound films, including the famous 1939 version starring Basil Rathbone and Nigel Bruce.
* Modern Adaptations: We also have contemporary versions like the 2002 film with Patrick Stewart.
Television:
* Classic TV: There were several adaptations for British and American television in the 1950s and 60s.
* Modern TV: More recent versions include a BBC adaptation in 2002, and various television series that feature the story as an episode, like Sherlock (2012) and The Adventures of Sherlock Holmes (1984).
Other Media:
* Radio: Many radio adaptations exist, dating back to the 1930s.
* Stage: The story has been adapted for the stage numerous times.
Adding it all up: The total number of film and TV versions is easily in the dozens, if not more if you include all the radio and stage adaptations.
Keep in mind:
* This list only covers major adaptations. There are likely countless lesser-known productions, especially short films and amateur productions.
* It's also worth noting that some adaptations have been re-released or remastered multiple times, further increasing the count.
It's safe to say that The Hound of the Baskervilles has been a popular story for adaptation for over a century and continues to be revisited in new and exciting ways.