Group B beta-haemolytic streptococcus (GBS) is the leading cause of life-threatening perinatal infection in developed countries. As immunization of women is not yet available, selective intrapartum chemoprophylaxis appears to be the best current strategy for preventing disease. All pregnant women should be screened for GBS at 26 to 28 weeks gestation. During labour, all colonized women with risk factors for invasive GBS neonatal infection should be treated with intravenous penicillin or ampicillin. Risk factors include preterm labour, premature rupture of membranes, intrapartum fever, multiple births, prolonged rupture of membranes, maternal diabetes, previous sibling with invasive GBS disease, and maternal GBS bacteriuria. The latter two categories warrant chemoprophylaxis regardless of maternal colonization status.