The use of antibiotics to prevent infections during pregnancy and the puerperium is clearly different from the use of antibiotics to treat established infections. Prophylactic antibiotics are frequently prescribed on an "empiric" basis, which for many years was thought to have few adverse consequences. Concerns about the emergence of resistant strains of common bacteria, in addition to the emergence of strains with increased virulence, have resulted in increased scrutiny of the use of antibiotics, particularly in the hospital setting. Cost considerations also affect the use and choice of prophylactic agents. The purpose of this Practice Bulletin is to present a review of clinical situations in which prophylactic antibiotics are frequently prescribed and to weigh the evidence supporting the use of antibiotics in these scenarios.