Group B streptococcal disease is the commonest cause of early-onset neonatal sepsis in most developed countries. Recent epidemiological studies and controlled trials have shown that many cases are theoretically preventable and guidelines have been widely adopted in the United States and Australia but are not common place in much of Europe. Infections caused by group B streptococcus may present at any time before, during or after delivery. This article reviews aspects of early-onset sepsis in the newborn infant (clinical presentation in the first 48 hours) as almost all of these cases are maternally acquired. Microbiological, epidemiological, pathophysiological and clinical aspects of the disease are discussed, and the practical implications of adopting preventative programmes are addressed.