Mechanical ventilation is a life-saving invasive procedure performed in intensive care units (ICUs) where critical patients are given advanced support. The purpose of this study was to assess the effect of personnel training on the incidence of ventilator-associated pneumonia (VAP). The study, performed prospectively in the ICU, was planned in two periods. In both periods, patient characteristics were recorded on patient data forms. In the second period, ICU physicians and assistant health personnel were given regular theoretical and practical training. Twenty-two cases of VAP developed in the pre-training period, an incidence of 31.2. Nineteen cases of VAP developed in the post-training period, an incidence of 21.0 (P<0.001). Training reduced development of VAP by 31.7 %. Crude VAP mortality was 69% in the first period and 26% in the second (P<0.001). Statistically significant risk factors for VAP in both periods were prolonged hospitalization, increased number of days on mechanical ventilation, and enteral nutrition; risk factors determined in the first period were re-intubation, central venous catheter use and heart failure and, in the second period, erythrocyte transfusion >5 units (P<0.05). Prior to training, compliance with hand washing (before and after procedure), appropriate aseptic endotracheal aspiration and adequate oral hygiene in particular were very low. An improvement was observed after training (P<0.001). The training of personnel who will apply infection control procedures for the prevention of healthcare-associated infections is highly important. Hand hygiene and other infection control measures must be emphasized in training programmes, and standard procedures in patient interventions must be revised.