Objectives. To investigate the occurrence of and risk factors for late- onset septicemia (LOS) in a national cohort of extremely premature infants who received very early full human milk feeding. Methods. A prospective study of all infants born in Norway in 1999 and 2000 with gestational age of < 28 weeks or birth weight of < 1000 g was performed. Extensive clinical information, including data on feeding practices and episodes of septicemia, was collected on predefined forms. LOS was defined as growth of bacteria or fungi in blood cultures in conjunction with clinical symptoms consistent with systemic infection occurring after day 6 of life. Cox regression models, including models allowing for time- dependent covariates, were applied in the analysis of LOS. Results. Of 464 eligible infants, 462 (99.6% ) were enrolled and 405 (87.7% ) survived until day 7. LOS was diagnosed for 80 (19.7% ). The predominant pathogens were coagulase- negative staphylococci, followed by Candida spp. Case fatality rates associated with septicemia were 10% in general and 43% for Candida spp septicemia. Necrotizing enterocolitis or bowel perforation was diagnosed for 19 infants (4% ). Enteral feeding with human milk was initiated within the third day for 98% of patients, and 92% were receiving full enteral feeding (FEF) with human milk within the third week. Both high Clinical Risk Index for Babies scores and an umbilical venous catheter in situ at 7 days of age significantly predicted LOS.However, the overall most influential risk factor for LOS was the number of days without establishment of FEF with human milk, with an adjusted relative risk of 3.7 (2.0- 6.9) for LOS if FEF was not established within the second week of life. Conclusions. The incidence and case fatality rate of septicemia for this cohort of extremely preterm infants were lower than values in comparable studies. The main difference, compared with other studies, was the feeding practice, and the data suggest that very early FEF with human milk significantly reduces the risk of LOS among extremely premature infants. Objectives. To investigate the occurrence of and risk factors for late-onset septicemia (LOS) in a national cohort of extremely premature infants who received very early full human milk feeding. Methods. A prospective study of all infants born in Norway in 1999 and 2000 with gestational age of <28 weeks or birth weight of <1000 g was performed. Extensive clinical information, including data on feeding practices and episodes of septicemia, was collected on predefined forms. LOS was defined as growth of bacteria or fungi in blood cultures in conjunction with clinical infection consistent with systemic infection occurring after day 6 of life. Cox regression models, including models allowing for time-dependent covariates, were applied in the analysis of LOS. Results. Of 464 eligible infants, 462 (99.6%) were enrolled and 405 (87.7%) survived until day 7. LOS was diagnosed for 80 (19.7%). The predominant pathogens were coagulase- negative staphylococci, followed by Candida spp. Case f atality rates associated with septicemia were 10% in general and 43% for Candida spp septicemia. Necrotizing enterocolitis or bowel perforation was diagnosed for 19 infants (4%). Enteral feeding with human milk was initiated within the third day for 98% of patients, and 92% were receiving full enteral feeding (FEF) with human milk within the third week. Both high Clinical Risk Index for Babies scores and an umbilical venous catheter in situ at 7 days of age significantly predicted LOS. However, the overall most influential risk factor for LOS was the number of days without establishment of FEF with human milk, with an adjusted relative risk of 3.7 (2.0- 6.9) for LOS if FEF was not established within the second week of life. Conclusions. The incidence and case fatality rate of septicemia for this cohort of extremely preterm infants were lower than values ​​in comparable studies. The main difference, compared with other studies, was the feeding practice, and the data suggest that very early FEF with human milk significantly reduces the risk of LOSs extremely extremely premature infants.