Objectives. To investigate the incidence, causes, predictors, and outcomes of septicemia in the first week of life in a national cohort of extremely premature infants. Methods. A prospective study of survival of all infants with gestational age of < 28 weeks or birth weight of < 1000 g who were born in Norway in 1999- 2000 was performed. Data on the maternal prenatal history, delivery, and neonatal course, including detailed information on episodes of microbiologically verified septicemia, were collected on predefined forms. Septicemia was reported in 2 groups, ie, episodes diagnosed on the day of delivery (ie, very early- onset septicemia [VEOS]) and episodes diagnosed from day 2 to day 7 of life (ie, early- onset septicemia [EOS]). Logistic regression models were used for the selection of variables for predictor analysis in each group. Results. Of 462 included infants, VEOS occurred for 15 (32.5 per 1000 population) and EOS for 15 (35.5 per 1000 population). The most prevalent bacteria were Escherichia coli in VEOS (n=9) and staphylococci (coagulase- negative staphylococci and Staphylococcus aureus) (n=15) in EOS. Case fatality rates were 40% and 13% , respectively. Independent predictive factors for VEOS were clinical chorioamnionitis (odds ratio [OR]: 10.5; 95% confidence interval [CI]: 3.3- 33.4) and high maternal age (OR: 1.2; 95% CI: 1.0- 1.3), whereas not receiving systemic antibiotic therapy within 2 days of age (OR: 13.6; 95% CI: 3.7- 50.2) and receiving nasal continuous positive airway pressure (n- CPAP) support at 24 hours of age (OR: 9.8; 95% CI: 2.5- 38.4) independently predicted septicemia after the first day of life. Conclusions. Whereas vertically transmitted septicemia was dominated by Gram- negative bacteria, with predictors being exclusively of maternal origin, EOS was dominated by typically nosocomial flora, with n- CPAP treatment at 24 hours of age being a powerful predictor. Early n- CPAP treatment, as opposed to mechanical ventilation, as a powerful predictor of septicemia in the early neonatal period,even with adjustment for early systemic antibiotic treatment, is a new observation among extremely premature infants that warrants additional study. Objectives. To investigate the incidence, causes, predictors, and outcomes of septicemia in the first week of life in a national cohort of extremely premature infants. Methods. A prospective study of survival of all infants with gestational age of <28 weeks or birth weight of <1000 g who were born in Norway in 1999-2000 was performed. Data on the maternal prenatal history, delivery, and neonatal course, including detailed information on episodes of microbiologically verified septicemia, were collected on predefined forms. Septicemia was reported in 2 groups, ie, episodes diagnosed on the day of delivery (ie, very early-onset septicemia [VEOS]) and episodes diagnosed from day 2 to day 7 of life (ie, early- onset septicemia [EOS]). Logistic regression models were used for the selection of variables for predictor analysis in each group. Results. Of 462 included infants, VEOS occurred for 15 (32.5 per 1000 population) and EOS for 15 (35.5 per 1000 population). The most prevalent bacter ia were Escherichia coli in VEOS (n = 9) and staphylococci (coagulase- negative staphylococci and Staphylococcus aureus) (n = 15) in EOS. Case fatality rates were 40% and 13%, respectively. Independent predictive factors for VEOS were clinical chorioamnionitis (odds ratio [OR]: 10.5; 95% confidence interval [CI]: 3.3-33.4) and high maternal age (OR: 1.2; 95% CI: 1.0-1.3) (OR: 13.6; 95% CI: 3.7-50.2) and receiving nasal continuous positive airway pressure (n- CPAP) support at 24 hours of age (OR: 9.8; 95% CI: 2.5-38.4) independently predicted septicemia after the first Whereas vertically transmitted septicemia was dominated by Gram-negative bacteria, with predictors being exclusively of maternal origin, EOS was dominated by typically nosocomial flora, with nCPAP treatment at 24 hours of aging being a powerful predictor. Early n-CPAP treatment, as opposed to mechanical ventilation, as apowerful predictor of septicemia in the early neonatal period, even with adjustment for early systemic antibiotic treatment, is a new observation of extremely premature infants that warrants additional study.