Background:Nosocomial pneumonia (NP) is a common complication in mechanically-ventilated patients and is considered to be one of the most common causes of morbidity and mortality. However, assessment of the associated mortality is not staightforward as it shares several risk factors with NP that confound the relationship. The aim of this study was to evaluate the impact of NP on the mortality rate in an intensive care unit. During the study period (January-December 1995) all patients under mechanical ventilation for a period > 48 h (n = 314) were prospectively evaluated, and the prognostic factors of NP, which have been identified in previous studies, were recorded.Results:Pneumonia was diagnosed in 82 patients. The overall mortality rate was 34% for patients with NP compared to 17% in those without NP. Multivariate analysis selected the following three prognostic factors as being significantly associated with a higher risk of death: the presence of multiple organ failure [odds ratio (OR) 6.71, 95% CI, P < 0.001]; the presence of adult respiratory distress syndrome (ARDS) (OR 3.03, 95% CI, P < 0.01), and simplified acute physiology score (SAPS)> 9(OR 2.89, 95% CI, P < 0.05).Conclusions:In mechanically-ventilated patients NP does not represent an independent risk factor for mortality. Markers of severity of illness were the strongest predictors for mortality.