A one-year, prospective, two-observational cohort study was performed to evaluate the incidence and outcome in hospitalized patients (ICU and non-ICU) of nosocomial bacteraemia, and to assess its prognostic value in the ICU group. A group of 18 098 hospitalized patients and a group of 291 consecutive ICU patients were followed. Prognostic factors were determined using single and multivariable analyses. 109 (90 non-ICU and 19 ICU) patients developed 118 nosocomial bacteraemic episodes. The incidence of nosocomial bacteraemia was 6.0 per 1000 admissions (95% confidence interval (CI): 5-7%) and 65 per 1000 admissions in ICU patients (95% CI: 4.5-8.5%). Gram-positive and Gram-negative bacteria were 63/133 (47%) and 70/133 (53%) of the isolated micro-organisms respectively. Crude mortality rates were 41/109 (38%) with adverse outcome associated with mechanical ventilation (OR: 3.6; 95% CI: 1.4-9.2, P =0.01), neutropenia (OR: 7.7; 95% CI: 0.8-73.1;P =0.07) while gastro-intestinal surgery was associated with an improved outcome (OR: 0.4; 95% CI: 0.16-0.96;P =0.04). Of the 291 ICU patients, 19 acquired 22 episodes of nosocomial bacteraemia, and 18 were referred from the wards with documented nosocomial bacteraemia. Of these 37 bacteraemic patients, 17 (46%) died. When adjusting for predictors of death (SAPS II>/=40, cardiac and neurological failure), nosocomial bacteraemia markedly influence the outcome in ICU patients (OR: 3.4; 95% CI: 1.3-8.7;P =0.010). This study suggests that the outcome of nosocomial bacteraemia in hospitalized patients is poor in ventilated and neutropenic patients and that nosocomial bacteraemia per se influenced outcome in ICU patients.