A 72-year-old man with subacute right upper limb palsy was diagnosed with cerebral infarction at another hospital. However, the head magnetic resonance imaging (MRI) scans showed no abnormalities. He was later transferred to our hospital because of cognitive dysfunctions. Because his symptoms had gradually worsened, a second head MRI was performed on admission. The scans showed an abnormality in the left frontal-parietal lobe, and the serum measles IgM level was elevated. Measles encephalitis was consequently diagnosed and steroid pulse therapy was immediately initiated. The patient recovered with no limb palsy or cognitive dysfunctions. With widespread administration of the measles vaccine, we expect that the incidence of modified measles will increase in the future. Hence the serum titer of the measles virus should be measured when patients with subacute meningoencephalitis of unclear origin are identified.