In the last few years the importance of GBS as the cause of serious neonatal sepsis has become more evident. The number of cases of this infection clearly exceeds the number of other congenital infections, for which antenatal screening is performed. Asymptomatic colonization of the genital tract of the pregnant woman has the most important role in transmission of GBS and several risk factors are connected to neonatal infection. In order to assess the epidemiological situation in Tuscany, 5079 pregnant women have been recruited by the Obstetrical Department of 16 Hospitals and evaluated for the vaginal colonization by GBS. 3654 couples mother-neonate have also been studied to ascertain the transmission of this germ to the neonate. A vaginal swab was collected at the admission to the Hospital at delivery-time and swabs from several sites of the neonate were obtained just after birth. A blood-agar culture and a latex agglutination test were employed to detect the GBS. GBS was present in 6.6% of the vaginal cultures, with a wide variation in colonization rates. 2.2% of the neonates were positive. The transmission of GBS from the positive mother to the neonate occurred in 20% of the cases. Furthermore one positive neonate out of three was born from a negative mother. No correlation between GBS positivity and preterm delivery was found. The rates of prevalence of GBS in our population, both mother and neonates, suggest a situation that can no longer be neglected. Our data are probably underestimated because of the low sensibility of the culture method. A preventive strategy has to be employed to avoid serious neonatal sepsis. An antenatal screening that provides a vaginal culture at the 36th week of gestation and a chemoprophylaxis intra-partum in the positive cases appears to be the most effective approach.