Neurologic illness associated with acute St. Louis encephalitis, West Nile, and Japanese encephalitis virus infection includes acute aseptic meningitis, encephalomyelitis, and a poliomyelitis-like syndrome. Few post-infectious immune-mediated neurologic events associated with flaviviral infection have been reported. The authors report on a woman with apparent post-infectious encephalomyelitis associated with recent St. Louis encephalitis virus infection, suggesting that neurologic illness from flaviviruses may also be seen in the post-infectious period following mild clinical illness.