The patient was an 11-month-old boy who developed encephalopathy associated with respiratory syncytial virus bronchiolitis. Right hemispheric encephalopathy was indicated by left hemiparesis and a diffuse right hemispheric lesion detected with magnetic resonance imaging. Elevated levels of interleukin-6 in the cerebrospinal fluid during the acute phase suggested the involvement of increased production of one or more cytokines in the pathogenesis of viral related encephalopathy, similarly to that proposed for influenza encephalopathy.