GOAL: The goal of this study was to assess the clinical significance of APACHE II scoring system in patients with VAP, as well as its relationship to treatment outcome, lenght of stay in ICU and lenght of artificial ventilation. PARTICIPANTS AND METHODS: The study was designed as a retrospective, observational study. Study was conducted in Clinic of Anaestesiology and intensive treatement of Clinical Hospital Center Split. The data in the study are collected from patient′s medical resords and other prelevant medical documentation pertinent to the treatment, in period of January 1, 2011 to December 31, 2011. In the study were included 406 patients in accordance to exact inclusion and exclusion criteria. The following variables were analysed: demographic data, APACHE II scoring systems, the incidence of ventilator-associated pneumonia, pathogens responsible for VAP, duration of mechanical ventilation, length of stay at the ICU and outcomes of treatment. RESULTS: Ventilation-associated pneumonia (VAP) was diagnosed in 104 (26%) participants or incidence rate was 22 VAP per 1 000 ventilator-days. Analysis have shown a statistically significant difference in influence of the severity (meassured by APACHE II (P=0.04) scoring systems) on the incidence of ventilation-associated pneumonia. We didn't found a statistical significance in the distribution of participants by ventilation-associated pneumonia to treatment outcome (P=0.192). There was a statistically significant correlation between the number of points of severity of illness by APACHE II (P<0.001) with the outcome, especially mortality outcome. From the analysis of the correlation coefficient we have proved that there is a slight but statistically significant positive correlation between length of hospital stay (P=0.003) and duration of mechanical ventilation (P<0.001) with APACHE II scoring system. The length of stay at the ICU is positive correlated with duration of mechanical ventilation (P<0.001), as the ventilation-associated pneumonia with the length of stay at the ICU (P<0.001) and duration of mechanical ventilation (P<0.001). CONCLUSIONS: The study shows that the severity of illness, expressed or meassured by APACHE II scoring system, was significant risk factor for the development of ventilation-associated pneumonia, and more significant predictors of hospital mortality in the ICU than that of survival. The length of stay at the ICU and duration of mechanical ventilation have significantly positive correlation with severity of patients' status, meassured by APACHE II scoring system, and the development of ventilation-associated pneumonia prolonged statistical significance the duration of mechanical ventilation, as well as the length of stay at the ICU.