Background: Group B streptococcus (GBS) is an important cause of neonatal sepsis. Guidelines advise to collect cultures at 35-37 weeks' gestation and to administer intrapartum antibiotic prophylaxis in case of GBS-positive cultures, as well as in all preterm deliveries. Improved effectiveness of antenatal cultures might help to further decrease GBS early-onset disease. Objective: To determine the best timing of antenatal cultures, which may help establish optimal prevention of perinatal GBS infection in both term and preterm neonates. Methods: PubMed and EMBASE databases were searched for relevant articles published from 1966 to February 2009. Nine articles were included. Information about study features and predictive values of antenatal cultures were abstracted. Results: Positive predictive values for antenatal GBS cultures ranged from 43 to 100% (mean 69%) and negative predictive values from 80 to 100% (mean 94%). GBS cultures collected in late pregnancy had high positive predictive values for colonization during delivery. The negative predictive value was high and relatively constant regardless of GA. Conclusions: This systematic review confirms recommendations to screen pregnant women for colonization of GBS at 35-37 weeks' gestation, but one should be aware of the limitations of screening, with 6% of GBS carriers remaining undetected in antenatal cultures.