Was The Hound of the Baskervilles by Conan Doyle a children's book or an adult book?

Arthur Conan Doyle’s Hound of the Baskervilles was originally published in The Strand Magazine as a serial (the individual chapters were published over several months). After its publication in The Strand Magazine, it was published as a complete novel. The Strand Magazine published fiction and non-fiction articles and was targeted at adult readers. Further, Sherlock Holmes stories had a large adult audience at the time of their publication. Thus, it seems safe to conclude that the intended audience of The Hound of the Baskervilles at the time of its publication was adult readers.

It is also worth noting that some of the themes found in the novel (e.g., seemingly demonic animals, alleged curses, use of a spouse as a sexual lure, etc.) are of an adult nature and may not have been recognized or fully understood by younger readers of the time. This provides additional evidence for concluding that the intended audience for the novel was adult readers.

For readers today, The Hound of the Baskervilles works as both young adult and adult fiction. Changing cultural perceptions has led to younger audiences being better able to understand and process the adult themes in the novel. Indeed, the adult situations in The Hound of the Baskervilles seem quite tame compared with modern young adult horror and romance fiction.