This was the first adaptation where Sherlock Holmes uttered the phrase, "Elementary, my dear Watson", which was never uttered in the original stories.
Based on an 1899 stage play by William Gillette which--famously--was the stage debut of Charles Chaplin, playing the character of Billy. Terry Kilburn plays the character in the film.
The film was released on September 1, 1939, the same day as the German invasion of Poland.
This is the last time Basil Rathbone would wear the famous deerstalker hat and cape in the 14 Holmes films, though you can still see the hat hanging on the hat stand in the early Universal Holmes movies.
Holmes rewards Billy with a sixpence, and Billy exclaims, "Blimey, a tanner!" Tanner was a slang word for the pre-decimalization silver sixpence.