Paralytic poliomyelitis was diagnosed clinically in a 29-year-old man three weeks after his 2-year-old son received trivalent live oral poliovirus vaccine. Type 2 poliovirus with "vaccine-like" characteristics was isolated from the patient's stool, and the serum showed a significant rise in neutralizing antibody against type 2 virus. There was no rise in complement fixation antibody titers. The patients illness was likely due to type 2 poliovirus contracted from his son. Physicians should inquire about the immunization status of parents before administering vaccine to children.