Background. - Nosocomial bloodstream infections in pediatrics are an important cause of morbidity and mortality. To identify pathogens causing nosocomial bloodstream infections, evaluate associated risk factors and take preventive measures, we conducted a prospective study from January 1995 to December 1995 at Saint-Vincent-de-Paul Hospital (Paris). Patients and results. - All patients hospitalized more than 48 hours were included in the study. During this period, we recorded 21 bloodstream infections in 20 children. The incidence rate of nosocomial bloodstream infection was 1/1,000 admissions. Sixteen children were hospitalized in surgery, three in medical intensive care unit; the median day onset of infection was approximately 20 days. Recorded risk factors were: surgery invasive procedures, central cathetarization, bladder catheters, parenteral nutrition, device, endotracheal tube, antibiotic therapy before infection. The number of risk factors ranged from zero to sir per patient. The most common isolated pathogens were in ten cases Gram positive cocci: five methicillin-sensible Staphylococcus aureus, four methicillin-resistant coagulase-negative staphylococci and one Streptococcus milleri. Other bacteria were seven enterobacteria, three Pseudomonas sp and three Candida sp. In II cases, the same bacteria as in bloodstream infection could be found: in three urine samples, in two tracheal samples, in two gastro-intestinal samples, two puncture sites one device, and one umbilical catheter. Conclusion. - In our study, 6.2% of positive blood culture were due to a nosocomial infection. We confirm the importance of Gram positive cocci, and particularly of methicillin-resistant coagulase negative staphylococci. (C) 1998 Elsevier, Paris.