Continuity mistake: During Larry Talbot's first transformation into the Wolf Man in the hospital, he goes from wearing light-colored pajamas to a dark shirt and pants. When he awakens the next morning, he's back wearing the pajamas.
Factual error: When the moon starts to rise as Larry is lying in the hospital bed, the light from the moon is shown moving from the floor up to his bed. Since the moon is appearing from the horizon, the light should be moving from the wall down to the floor.
Other mistake: Despite the early scenes being set in Cardiff and its environs, not one character has a South Wales accent.