Rasmussen's encephalitis (RE) is a rare and progressive neurologic condition of uncertain etiology that typically has a childhood onset. The authors describe a 45-year-old woman with adult-onset progressive aphasia, right hemiparesis, severe drug refractory epilepsy, and left cerebral hemisphere atrophy. High-dose corticosteroids and plasmapheresis were not effective. She improved with high-dose therapy with human IV immunoglobulin.