We evaluated whether prophylactic nebulised colistin could reduce ventilator-associated pneumonia (VAP) rates in an intensive care unit (ICU) setting with prevalent multidrug-resistant (MDR) bacteria.We used a single-centre, two-arm, randomised, open-label, controlled trial in a 12-bed ICU in the University Hospital of Larissa, Greece. Patient inclusion criteria included mechanical ventilation of >48 h. The two arms consisted of prophylaxis with 500 000 U colistin (Col group) or normal saline (NS group), thrice daily, for the first 10 ICU days or until extubation. The primary outcome of the study was the 30-day VAP incidence.In total, 168 patients entered the study. VAP incidence was not different between Col and NS group patients (14 (16.7%) versus 25 (29.8%), respectively, p=0.07). Regarding the secondary outcomes, the intervention resulted in a lower VAP incidence density rate (11.4 versus 25.6, respectively, p<0.01), and less Gram-negative bacteria-VAP (p=0.03) and MDR-VAP (p=0.04). Among VAP patients (n=39), prophylaxis with inhaled colistin improved ICU survival (p=0.016). There was no evidence of increased resistance to colistin or multidrug resistance.Our findings suggest that nebulised colistin had no significant effect on VAP incidence.