When crew members suggested to Roman Polanski that perhaps the film was too unrealistically gory for its own good, Polanski reportedly replied, "I know violence. You should've seen my house last summer."
During the set up of the gruesome death scene of Lady MacDuff's children, director Roman Polanski was instructing a four-year-old blonde girl on how to play dead, while smearing tons of fake blood all over her body. Polanski playfully asked the girl what her name was, to which she replied, "Sharon".
Roman Polanski wanted to include a violent bear-baiting sequence but it posed all kinds of problems. The first bear they tried to use was too timid and kept running away from the dogs, while the second was uncontrollably vicious and pawed a crew member. He eventually opted for an intrepid stuntman in a bear suit, but understandably the man would only agree to a single dog being set loose on him, fearing his armored padding wouldn't be up to the job. Polanski secretly instructed the handlers to loose three dogs, sending the stuntman cowering in fear, screaming at the director to call them off.
Director Roman Polanski's wife, actress Sharon Tate, was murdered by Charles Manson three years before the making of the film. It is believed that due to this traumatic event, Polanski developed the story to be a more violent representation of Shakespeare's play. For instance, the scene in which Macbeth murders King Duncan was not in the original play and was instead implied.
In her memoirs Marianne Faithfull recalls screen testing for the role of Lady Macbeth at the request of Roman Polanski. However when her heroin use became obvious to Polanski during the test she lost the role.
When Roman Polanski was casting the film, his co-screenwriter Kenneth Tynan suggested Nicol Williamson for the title role. Tynan was a great admirer of Williamson, but Polanski turned him down because he thought Williamson lacked sex appeal. Williamson later played Macbeth in London and on Broadway and for the B.B.C.