In a retrospective study of neonatal septicaemia and meningitis in a defined region of western Sweden 1975-1986, 231 cases were identified. The incidence was 2.8/1000 live births. The case-fatality rate was 15%. thirty-three patients had meningitis. Only 55 patients (24%) had no known risk factors. Preterm delivery was a most important risk factor for both morbidity and mortality. The most common causative organisms were group B streptococci, Staphylococcus aureus and aerobic Gram-negative rods, together isolated from 82% of the patients. The cases were approximately equally divided between very early, early and late onset infections. Group B streptococci were over-represented in very early onset infections in all birthweight groups and aerobic Gram-negative rods were the most common isolates from low birthweight infants with late onset infections. However, group B streptococci, Staphylococcus aureus and Gram-negative rods were found in all birthweight and gestational age groups. Thus, initial antimicrobial therapy must be equally broad in all neonates with suspected septicaemia.