The first MGM release to get an X rating from the MPAA.
The second of four times that Thorley Walters played Watson, each with a different actor playing Sherlock Holmes. He previously did so in Sherlock Holmes and the Deadly Necklace (1962) starring Christopher Lee and later did so in The Adventure of Sherlock Holmes' Smarter Brother (1975) starring Douglas Wilmer and Silver Blaze (1977) starring Christopher Plummer.
Originally planned as a star vehicle for producer Carlo Ponti's wife, Sophia Loren, as "Best House in Milan" with either Marcello Mastroianni or Vittorio Gassman as her costar.
Real life people portrayed in the movie, whose characters are ostensibly walk-on/walk-offs with one line of dialogue apiece, include Charles Dickens, Alfred Lord Tennyson, Oscar Wilde, Lord Alfred Douglas, Lady Emilia Dilke, Algernon Charles Swinburne, a pre-Browning Elizabeth Barrett Browning, and Dr. David Livingstone. One other real life person who is mentioned to have a direct association with one of the movie's characters is Florence Nightingale.