During a widespread epidemic of Japanese encephalitis, five pregnant women affected by the illness were observed. The diagnosis of Japanese encephalitis virus (lEV) infection was established on the basis of clinical presentation, rising titers of hemagglutination-inhibiting antibody, and the presence of specific IgM antibodies. Two women aborted, two were delivered of apparently normal children, and the fate of one case is not known. From brain, liver, and placental tissues of one of the aborted fetuses, JEV was isolated. This appears to be the first report of human transplacental infection with JEV.