Nosocomial bloodstream infection (BSI) is a common finding in cardiac surgery intensive care units and is associated with excess mortality and hospital costs. Additional data are needed about incidence, characteristics, predictors, associated microorganisms of nosocomial BSI in cardiac surgical patients in order to refine measures to prevent nosocomial infections and to improve recovery outcomes in this patient population. The 3912 cardio-thoracic surgery patients from all age groups were admitted to the study at the Gottsegen György Hungarian Institute of Cardiology between January 1999 and December 2000. In each patient with BSI demographic, epidemiological and clinical variables were recorded along with potential risk factors. Incidence of associated pathogens and their possible sources were evaluated and outcome and mortality risk factors were assessed. There were a total of 134 episodes of BSI. The incidence was 34.25 per 1000 admissions. The leading microorganisms were staphylococci (37.7%). Bacteremic episodes developed secondary to an identifiable source in 27.6% of the cases, or were catheter-related (16.4%). In 56% of the cases the source was not identified. The crude mortality rate was 33.3%. Higher mortality rate was associated with intracardial grafts (p < 0.05), low left ventricular ejection fraction (p < 0.04), diabetes mellitus (p < 0.05), an age above 16 years (p < 0.02), severe sepsis (p < 0.001) and high APACHE II score (p < 0.001). As the identified main sources of BSI were intravascular lines, mortality from BSI could probably be reduced by paying more attention to the prevention, early recognition and prompt management of intravascular device associated infections.