Trivia

Director Harry Kümel was a passionate admirer of Orson Welles and had him in mind for the role of Cassavius right from the beginning. According to him, it was pretty easy to convince Welles to take the part, once they assured to pay him the salary he asked for. Looking forward to meet and direct his idol, Kümel was pretty nervous when walking onto the set - just to find out that Welles was in a bad mood and drunk. He later stated in interviews that he personally got along well with Welles during the rest of the shoot but the majority of the crew didn't and tried to get out the grumbling Welles' way most of the time.

This film was Harry Kümel's favorite project for a long time but it was not until his previous film Daughters of Darkness (1971) succeeded at the box office (most notably in the US) that he managed to raise funding for it. Unfortunately, "Malpertuis" did poorly in most countries, though it was even nominated for the Palme d'Or at the Cannes Film Festival.

Susan Hampshire's nude scenes as "Alice" and "Euryale" used a body double.

Charles Higham's derogatory biography of Orson Welles, subtitled "The Rise And Fall Of An American Genius", devotes one page to three photographs of Welles, said to show him at the ages of five, thirty-six and sixty-seven. There is no comment on the photos, but the change in Welles' appearance is most noticeable, the third photograph showing a dissolute and depraved-looking ancient, clearly near death, gross and corrupt. But, in fact, this image is not taken from life, like the other two, but is a still from this film, where Welles plays a 100-year-old master criminal depicted on his deathbed; he is, in other words, supposed to look gross and corrupt and older than his actual years. Harry Kumel's film was barely shown at all in either Britain or America, and was a major flop in those parts of Europe where it was shown; Higham clearly assumed that no-one would spot it as a film still, and would merely make the derogatory assumptions he wanted his readers to make.

Orson Welles dubbed his own voice in the English Language version of the film.