Claire Clairmont (Myriam Cyr) falls out of the rowboat in the opening scene, but just a few seconds later, as she's running with Percy toward the house, her clothes and hair are totally dry.
Near the end, primates are shown in a cage on the lawn. In actuality, Lord Byron kept all of his many animals in the house with him. Only his horses were kept outside the house.
Dr. Polidori (Timothy Spall) attacks Percy Shelley (Julian Sands).Coming to Shelley's defense, Lord Byron (Gabriel Byrne) strikes Polidori (Timothy Spall) several times across the back with his cane. A square pad is readily noticeable under Polidori's shirt during this. It lasts for the entirety of the scene randomly disappearing and reappearing depending on the shot.