• Neonatal poliomyelitis, which was rare even when poliomyelitis was widespread, has not been reported in the United States since use of live oral poliovirus vaccine (Sabin's vaccine) became widespread. We report a child who became symptomatic with apnea at 18 days of age and who subsequently developed a permanent monoparesis. Serologic and cultural evidence indicated the virus as poliovirus vaccine type. Another infant who received live oral poliovirus vaccine was probably the source of the infecting virus. Recognition that poliovirus infection can still occur in the United States and an understanding of the serologic, cultural, and typing tests required to substantiate this diagnosis arc needed so that such patients will be accurately diagnosed.