Streptococcus agalactiae or group B streptococcus (GBS) is the most common cause of neonatal sepsis and meningitis in neonates. One of the major questions is whether the GBS strains able to cause neonatal invasive disease have peculiar genetic features. A collection of S. agalactiae strains, isolated from cervix, vagina and rectum of 10 mothers and from throat, ear and umbilicus of their newborns was genetically characterized by pulsed-field gel electrophoresis (PFGE). This study demonstrated that the strains isolated from each mother and her child were all genetically identical but that the strains from the 10 mother/child pairs mutually were genetically heterogeneous and 10 different PFGE patterns were found. Although it has been suggested that PFGE would be able to identify virulence traits to direct decisions in antibiotic management, the heterogeneous feature of GBS strains does not support broad application.