Charenton, the asylum depicted in the film, was established in 1645 and still exists and is still in use, although it is now called the Esquirol Hospital (l'Hôpital Esquirol), named for Jean-Étienne Dominique Esquirol, a French psychiatrist who ran the hospital in the 19th Century.
Several lines in de Sade's play give the impression that Charlotte Corday was a royalist (as she was portrayed, for instance, in the British press at the time of her trial). In fact she belonged to a revolutionary sect, the Girondins, more moderate than Marat's.
The October 30, 2005 edition of the comic strip "Frank and Ernest" started with Frank saying that the printing press was down and they would have to do all the posters for the Bijoux's double bill by hand. Frank, of course, assigned himself the poster for M (1931), and assigned Ernest the poster for "Marat/Sade," with the full title written out.