Mayhem, in law, a willful injury inflicted by one person on another and resulting in the loss or weakening of some member of the victim's body. The word has the same origin as maim. Since mayhem is a felony the person who inflicts the injury is subject to criminal prosecution. The victim may also sue in a civil court for damages.

Under English common law mayhem was an act that rendered the victim less able to fight and to defend himself. The loss of a leg, arm, finger, or eye fell within the definition of the crime, but the loss of the nose or an outer ear did not. Statutes have extended the meaning of mayhem to include any willful disfiguring of the body.