One in three women carry group B streptococci vaginally, which can infect the amniotic fluid even if the membranes are intact, or can infect the baby during delivery, causing sepsis, pneumonia, or meningitis. Very-low-birthweight infants are at much higher risk of infection or mortality, with up to 3% infected, and mortality rates of up to 30% even with immediate antibiotic treatment. Late-onset group B streptococcal infection begins after 7-9 days, and usually causes fever or meningitis, but is less often fatal compared with early infection.We conducted a systematic review and aimed to answer the following clinical question: What are the effects of prophylactic treatment of asymptomatic neonates less than 7 days old with known risk factors for group B streptococcal infection? We searched: Medline, Embase, The Cochrane Library and other important databases up to March 2007 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).We found twelve systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.In this systematic review we present information relating to the effectiveness and safety of the following interventions: different antibiotics, monitoring and selective treatment, and routine antibiotic prophylaxis.