A 4-year-old boy developed right hemiplegia and aphasia during Mycoplasma pneumoniae (M. pneumoniae) infection. Computed tomography of the brain showed a large cerebral infarction of the left temporal area. Carotid angiography revealed an obstruction of a branch of the left middle cerebral artery. The possible pathogenesis of central nervous system (CNS) symptoms due to M pneumoniae infection is discussed.