Rasmussen encephalitis is a chronic, progressive inflammation of the brain of unknown origin. Early diagnosis and treatment with immunoactive agents and/or hemispherectomy are sought to prevent the progressive cognitive decline that accompanies this disease. Combined anatomic and functional neuroimaging may serve to focus the diagnostic workup and to hasten brain biopsy for definitive diagnosis. Two biopsy proved cases of Rasmussen encephalitis are presented. The importance of MR imaging, single-photon emission computed tomography, and proton MR spectroscopy in the workup of this disease is discussed.