In a retrospective study at Son Dureta Hospital (Palma de Mallorca, Mallorca, Spain) of the period 1977-1991, 334 cases of culture-proven sepsis and/or meningitis in neonates born at the facility were identified. Overall, there was an incidence rate of 4.9 cases per 1,000 live births. The case-fatality rate was 7.5%. Infection was more frequent in infants of low birth weight, with the exception of infants with meningitis and infections due to group B Streptococcus and Listeria species. The patterns of predominance among bacterial pathogens that were isolated changed during the period studied. From 1977 to 1984, Klebsiella pneumoniae was the most frequent such isolate, but this frequency declined in the following years. Group B Streptococcus organisms and Staphylococcus epidermidis replaced K. pneumoniae as the predominant pathogens in early- and Staphylococcus epidermidis replaced K. pneumoniae as the predominant pathogens in early- and late-onset infections, respectively. The frequency with which other pathogens were isolated did not vary significantly during the study period. Invasive infection caused by Candida organisms was found in two patients. The incidence of infection due to group B streptococci has increased in the last few years (to 2.4 cases per 1,000 live births in 1991) and has become a significant problem that requires a thorough epidemiological evaluation.