[en] OBJECTIVE: To assess the temporal relationship between ICU-acquired infection (IAI) and the prevalence and severity of organ dysfunction or failure (OD/F). DESIGN AND SETTING: Observational, single center study in a mixed intensive care unit of a university hospital. PATIENTS: We analyzed 1,191 patients hospitalized for more than 2 days during a 2-year observation period: 845 did not acquire IAI, 306 of whom had infection on admission (IOA); 346 did acquire IAI, 125 of whom had IOA. MEASUREMENTS AND RESULTS: The SOFA score was calculated daily, both SOFAmax, the sum of the worst OD/F during the ICU stay, and SOFApreinf, the sum of the worst OD/F existing before the occurrence of the first IAI. The SAPS II and SOFA score of the first 24 h were significantly higher in patients with than in those without IAI. SOFApreinf of IAI patients was also higher than the SOFAmax of patients without IAI both in patients with (12.1+/-4.6 vs. 8.9+/-4.7) and those without IOA (9.2+/-4.0 vs. 6.7+/-3.5). SOFApreinf represented 85.7% of the value of SOFAmax in patients with IAI. SOFApreinf increased significantly with the occurrence of sepsis, severe sepsis, or septic shock during ICU stay. Severe sepsis and septic shock during ICU stay as well as SOFApreinf were part of the factors associated with hospital mortality. CONCLUSIONS: IAI is significantly associated with hospital mortality; however, its contribution to OD/F is minor. Moreover, severity of IAI seems to be related to previous health status.