Group B streptococcal (GBS) infection is still an important cause of morbidity and mortality in newborn infants. In The Netherlands, there are no published data on the incidence of neonatal GBS infection. We collected data of all infants with GBS disease during the first 3 months of life, as reported to the Dutch Paediatric Surveillance Unit (DPSU) during a period of 2 years (1997-98). Neonates with early-onset GBS disease (both sepsis and probable sepsis) were included for further analysis. The level of completeness of the DPSU data was determined by capture-recapture techniques. The incidence of early-onset GBS disease in The Netherlands in 1997-98, as calculated from the DPSU data, was 0.9 per 1000 live births. After correction for under-reporting, the incidence was estimated to be 1.9 per 1000 live births. The case fatality rate of early-onset GBS disease was only 5%. Despite the decrease in the mortality rate during the last decades, it remains a serious condition with potential irreversible brain damage. Therefore, formal guidelines for the prevention of neonatal early-onset GBS disease in The Netherlands were introduced in 1999. The data collected in this study may serve as baseline data for evaluation of the effect of these guidelines.