Critically ill patients who require mechanical ventilation are at high risk for development of pneumonia during the course of treatment. Ventilator-associated pneumonia leads to higher rates of mortality and morbidity, increased length of hospital stay, and higher hospital costs. The intubation that is necessary for mechanical ventilation impairs the patient's normal defense mechanisms for fighting infection. Impaired defenses, along with such risk factors as age of the patient, equipment used, and failure of the staff to wash hands increase the likelihood of colonization of the lower airways. Colonization and subsequent pneumonia commonly occurs from microaspiration of secretions from the oropharynx and gastrointestinal tract. In this article, the mechanism of microaspiration, diagnosis of ventilator-associated pneumonia, and nursing strategies to reduce the incidence of pneumonia are described.