Rasmussen's encephalitis (RE) is a chronic inflammatory disease of unknown origin that usually affects one hemisphere of the brain. Serial electroencephalographic (EEG) and magnetic resonance imaging (MRI) associated with magnetic resonance angiography (MRA) features specific for RE are rarely reported. By assessing the progression of RE revealed through EEG, MRI/MRA, and treatment results, the authors determined that RE is a focal epileptic syndrome characterized by chronic and progressive partial epileptic seizures, with specific changes in EEG and MRI/MRA findings.