We have assessed the evidence that closed tracheal suction systems (TSS) prevent ventilator-associated pneumonia (VAP), using a meta-analysis of randomized controlled trials (RCTs). We searched PubMed and Cochrane databases to identify RCTs that compared closed with open TSS for the management of mechanically ventilated (MV) patients. Nine RCTs were included in the meta-analysis. There was no difference in the incidence of VAP between patients managed with closed and open TSS [odds ratio (OR)=0.96, 95% confidence intervals (CI) 0.72-1.28]. There was no heterogeneity among the eligible trials (I2=0, 95% CI 0-0.65). The compared groups did not differ with respect to mortality (OR=1.04, 95% CI 0.78-1.39) or intensive care unit (ICU) length of stay [two RCTs: 12.3 (sd 1.1) vs 11.5 (1.4) days and 15.6 (13.4) vs 19.9 (16.7) days]. Suctioning with closed systems was associated with longer MV duration (weighted mean differences: 0.65 days, 95% CI 0.28-1.03) and higher colonization of the respiratory tract (OR=2.88, 95% CI 1.50-5.52) than open TSS. The available evidence suggests that closed as opposed to open TSS usage did not provide any benefit on VAP incidence, mortality, or ICU stay of MV patients.