The left and right sides of the brain are called hemispheres. Hemispherectomy is the removal of one side of the brain. This procedure is sometimes done on children who have severe forms of epilepsy, such as Rasmussen syndrome and Sturge-Weber disease. These conditions badly damage one side of the brain, cause frequent seizures and problems with physical and mental development, and do not respond well to drug treatment.

Hemispherectomy may completely prevent seizures and reverse delays in development that occur with some forms of epilepsy.

The surgery always causes some loss of movement and sensation on one side of the body and sometimes causes partial loss of vision in half of the visual field of each eye. However, most children with a large epileptic area on one side of the brain already have these problems before the surgery.