A hemispherectomy is a surgical procedure to remove, disable or disconnect one hemisphere of the brain. It is a very rare procedure of last resort to treat severe seizures that are localized in one area of the brain. It is generally only used when a patient's seizures cannot be controlled by medication and are severe and frequent enough to impair a major life function or put the patient's life at risk. It is generally not performed merely because a patient suffers frequent seizures if they otherwise have high mental functioning.