Group B Streptococcus (GBS) is an important cause of neonatal sepsis in many areas. Although incidence data are available for a minority of countries, the magnitude of illness due to this bacterium appears to vary substantially. Disease may vary due to the prevalence of asymptomatic GBS colonization, the virulence of circulating strains, the frequency of predisposing conditions such as low birth weight, or differences in obstetric practices. Approaches to prevention of neonatal GBS disease include administering antibiotics to high risk mothers intrapartum, use of intrapartum vaginal disinfectants, development of GBS vaccines, and nonspecific approaches. Determinants of prevention policies in a given area depend on the incidence of disease, the structure of health care delivery, cost-effectiveness, and cultural attitudes. Much GBS disease among newborns is now preventable, yet data on incidence are needed to guide selection of appropriate approaches to disease prevention.