Alien hand syndrome is condition that may occur after a stroke, brain tumor, brain aneurysm, or neurosurgery in which an individual has no control over a hand which instead acts on its own.

Symptoms of alien hand syndrome may include a feeling that the hand does not belong to its owner (alien hand sign); involuntary movements, such as one hand performing actions contrary to the other hand; a hand that performs activities not directed by the owner (anarchic hand) or levitating hand; and a feeling of having an extra limb (supernumerary hand). Individuals with alien hand syndrome may be groped by their own hand against their will, or they may slap the alien hand with their normal hand. The alien hand may grab things and not let go or even attempt to suffocate the patient.

There is currently no treatment for alien hand syndrome, which may go away on its own in minutes, hours, or days or last for years.