For cinematic purposes, passages from the original play were cut for time and some soliloquies changed to inner monologues for the sake of psychologic realism.
In Polanski's version, Macbeth and Lady Macbeth are played by actors younger than has been tradition. In the person of twenty-six-year-old Francesca Annis, Lady Macbeth is a softer, tamer woman than is usual.
Her strength and sanity crumble at a horrific pace when she, at last, is aware of the inescapable nightmare she has helped create. Polanski explained this by noting that "directors always present Lady Macbeth as a nagging *****. But people who do ghastly things in life, they are not grim, like a horror movie". In an audacious departure from Shakespearean convention, Lady Macbeth's famous sleepwalking soliloquy is performed in the nude.
The lyrics to the song that Fleance sings at Macbeth's banquet for Duncan at Inverness are taken from the poem "Merciles Beautè" by Geoffrey Chaucer. In the context of the film this extraneously inserted song is itself an anachronism, as Chaucer lived in the fourteenth century and Shakespeare's Macbeth historically takes place in the eleventh century.
The film's bleak ending is the most significant departure from Shakespeare's text. Although Malcolm is crowned as Scotland's rightful king, his concluding speech is omitted in favour of an abrupt, wordless scene showing his brother, Donalbain, returning from exile and entering the witches' lair, implying that he will seek their counsel in usurping King Malcolm as Macbeth usurped King Duncan, thus re-cycling internecine bloodshed. Throughout the story, Donalbain is shown as envious of Malcolm, perhaps even more than was Macbeth.
The ending recasts the story as a closed circuit of action suggesting that the tragedy will be repeated ad infinitum. It may explain Fleance's founding of the House of Stuart, the extinction of Duncan's line, and the