Treatment in the intensive care units has aggressive character. A lot of invasive diagnostic and treatment procedures are used in order to keep vital functions of the patients. Some complications are associated with treatment methods. Hospital acquired infections are the main cause of mortality. Since artificial lung ventilation is the most common invasive treatment method, ventilator-associated pneumonia is the most common hospital acquired infection. The development of hospital acquired infections is dependent on two independent pathophysiological factors: decreased patient immunity and colonization of patient cavities by bacteria. Ventilator-associated pneumonia causes almost half of intensive care units infections. The most etiologic organisms responsible for ventilator-associated pneumonia in Europe and North America are Pseudomonas species and Methicillin resistant Staphylococcus aureus. Diagnosis of ventilator-associated pneumonia is based on clinical and laboratory criteria (fever, leukocytosis, purulent endotracheal secretions) and pulmonary infiltrates on chest radiograms. Pathogen can be distinguished using invasive or noninvasive techniques. Antimicrobial resistance aggravates treatment of ventilator-associated pneumonia. Antibiotic treatment should be chosen on the ground of clinical data, hospital epidemiologic situation and most common pathogens. Prevention of ventilator-associated pneumonia is based on improving basic hygiene and nursing quality. Ventilator-associated pneumonia morbidity could be reduced by identification of risk factors and risk prevention.