A late summer outbreak of illness involving newborn infants and mothers is described. Seven infants and five mothers were studied. Although three enterovirus types were recovered from the infants, the outbreak was associated with infection by a variant of ECHO 11. Clinical signs included fever, diarrhea, upper respiratory disease, and aseptic meningitis. In three infants the antibody response significantly exceeded that of the mother. The evidence for an etiologic association of ECHO 11 infection with disease is reviewed.