Rasmussen's encephalitis, originally thought to be a chronic form of viral encephalitis, is now thought to be an autoimmune disease of the brain and is more properly termed Rasmussen's syndrome. Starting in one area of one side of the brain, the disease appears to gradually and progressively involve that side of the brain causing progressive and intractable focal seizures, a hemiparesis, and expressive aphasia when the left hemisphere is involved. Immune therapy with steroids, immunoglobulins, or plasmaphoresis provide only temporary relief from seizures. Neither antibodies to Glu-R3 nor cortical biopsy are helpful in the diagnosis. Hemispherectomy of one form or another is the only curative therapy, and there is no evidence that one form of hemispherectomy is preferable to another. Immuno-ablative therapy may be a therapy of the future.