During the UCLA Sherlock Holmes Restoration Project (1993-2003) they were unable to find any 35mm elements of the main title for this film. The restored version uses a blow-up from a used 16mm television syndication print which was dissolved into the proper point. The main title of the restored version shows a decrease in resolution, increased grain and a reduction in image registration.

The last of 14 films released from 1939-46 based on Arthur Conan Doyle's fictional consulting detective Sherlock Holmes starring Basil Rathbone as Holmes and Nigel Bruce as Dr. Watson. Rathbone was reportedly tired of playing the character. However, he would play Holmes on the stage, radio and television at various times the rest of his career.

Mention is made by Watson of two stories from the original canon; "A Scandal in Bohemia" and "The Solitary Cyclist."

The plot bears some similarities with Arthur Conan Doyle's "The Six Napoleons", in which a valuable article is hidden somewhere in London.

One of several titles in the Sherlock Holmes series whose original copyrights were apparently not renewed and have thereby fallen into public domain; as a result, seriously inferior copies are presently being offered by a number of VHS and DVD dealers who do not have access to original studio masters.

Last of four titles in Basil Rathbone's Holmes films to feature Ian Wolfe in a supporting role.

The song Holmes is playing in his study on the violin is "Danny Boy".

Laurel & Hardy fans will spot frequent nemesis Charlie Hall as a cab driver early in the movie.

At around the 67-minute mark, Lillian Bronson's character remarks that she has heard a picture that Leyland Hodgson's tour guide has described as a presentation to Dr. Samuel Johnson (1709-84) from (although he does not explicitly say by) Joshua Reynolds (1723-92) was in fact a gift to the doctor from Mrs [Hester] Thrale (1741-1821), and definitely not a Reynolds. She's more wrong than right: that "etching", so described, is from the oil painting "Milton" (1877/8) by Hungarian artist [Munkácsy Mihály] (1844-1900), and as of 2018 is to be found in the New York Public Library. The artist wasn't even born until Johnsnon, Reynolds and Thrale were all decades dead.

Visiting the Universal commissary for her lunch while still wearing Hilda Courtney's disguise, Patricia Morison was sternly ordered by the maitre d' to eat with the rest of the extras at the counter, rather than at the actors' tables.

The ploy of using a bogus fire to reveal the location of a hidden item is taken from "A Scandal in Bohemia" and connections are made between Mrs. Courtney and that story's villainess, Irene Adler.