"... when I came back [from Paris], it was an absolute disaster, the way it was cut. The whole prologue was cut, a half-sequence was cut. I had tears in my eyes as I looked at the thing...It was the most elegant picture I've ever shot."
Missing Episode: The film was envisioned as a collection of several short stories, with two more segments filmed but ultimately left out of the film to keep the running time down. One of them is included in some home video releases.
The original idea had four stories involved, two of which (one in which Watson solves a mystery on a cruise and one in which Holmes solves a murder in an upside-down room) were edited out. The latter featured Inspector Lestrade.
George Sanders was supposed to play Mycroft, but dropped out at the last minute and was replaced by Christopher Lee. Laurence Olivier was also considered for Mycroft.
Rex Harrison wanted to play Sherlock Holmes, but Wilder turned him down. Charlton Heston was also considered for Holmes, but Wilder would hear none of it. (Chuck did play Holmes in the stage play and the 1991 film version of The Crucible of Blood).
Word of Dante: The movie takes Holmes' older, smarter brother Mycroft and suggests that he was the head of the Secret Service, and that his frequent haunt, the Diogenes Club, was a front. In canon, neither are other than what they appear to be (a Brilliant, but Lazy civil servant and a club of reclusive eccentrics specifically), but this interpretation has become a popular one.