Intrapartum transmission of group A streptococcus has not been well documented. As the incidence of severe infections due to this organism has recently increased, it is important to assess if such transmission occurs. We observed two cases of severe neonatal infections due to group A streptococcus, one of which was fatal, that appeared to have been transmitted from the mother during birth. Perinatal prophylaxis, which has been recommended for infections due to group B streptococcus, should be evaluated for infections due to group A streptococcus.