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The opening and ending credits differ in order, and not all of the cast members listed in the opening credits are listed at the end with character names. According to the Filmfacts review, the picture was previewed at 115 minutes, the running time listed by several other reviews, but was released at 108 minutes, which was the running time of the viewed print. Fred Mustard Stewart's best-selling novel appeared in a condensed version in the March 1969 issue of Cosmopolitan magazine.
According to a January 30, 1969 Daily Variety news item, the filmmakers considered casting Julie Christie in the picture. Although Hollywood Reporter production charts include Amy Thomson in the cast, her appearance in the completed picture has not been confirmed. A modern source adds Anabel Shaw to the cast and credits Greg C. Jensen with the film's special effects. Several reviews compared The Mephisto Waltz unfavorably to the 1968 film Rosemary's Baby, which also dealt with a conspiracy perpetrated by Satanists (see below).
The Mephisto Waltz was the only theatrical feature film produced by Quinn Martin, a noted television producer. Although Martin did produce the 1962 picture The Scarface Mob (see below), that film was actually the theatrical release of a two-part episode of his popular television series The Untouchables.