Group B streptococcus is the major cause of neonatal sepsis in the United States. It is estimated that 2,000 infants die annually of syndromes related to group B streptococcus infection. In the early-onset syndrome, transmission is from mother to child, either in utero or during birth. Pneumonia is the most common presentation in infants who develop symptoms during the first seven days of life. The principal manifestation of late-onset infection is meningitis, which occurs in 85 percent of this group. Although group B streptococcus infection is normally remediable with penicillin therapy, rapid diagnosis and treatment are necessary to prevent the serious consequences of the disease. A vaccine is under development, although the cost-effectiveness of a widespread immunization program for a disease with such a low frequency is still unknown. The potentially serious outcomes of this infection, however, make it a major problem for physicians involved in neonatal care.