Hospital-acquired pneumonia is the second most frequent nosocomial infection and the first in terms of morbidity, mortality, and cost. In recent years, international societies and, most recently, the American Thoracic Society jointly with the Infectious Disease Society of America, have developed guidelines for the management of hospital-acquired pneumonia, health care-associated pneumonia, and ventilator-associated pneumonia. These guidelines include recommendations for risk stratification, initial and definitive antibiotic treatment, and prevention. The validation of these guidelines is important because it confirms that they can be used in clinical practice, as quality indicators, and as a standard of care. Several processes can be validated and are included in the guidelines, such as the accuracy of the prediction of microorganisms according to stratification criteria and the impact of guidelines on outcomes, including length of hospital and intensive care unit stay, duration of mechanical ventilation, complications, and in-hospital and 30-day mortality. Clinical studies have shown that the accuracy of predicting microorganisms according to risk stratification is reliable ( approximately 80% and approximately 90%). Three studies suggest that the implementation of guidelines, with a special emphasis on antibiotic treatment, improves several parameters of outcome. Only one study, using a before-and-after design, showed a decrease in 14-day mortality after guidelines implementation. A key issue for these studies is to modify recommendations according to local patterns of microbiology and drug resistance. In summary, implementation of guidelines for the management of hospital-acquired pneumonia and ventilator-associated pneumonia decreases the rate of initial inappropriate antibiotic treatment and decreased 14-day mortality in a study. More clinical studies to validate the influence of guidelines on outcome are warranted.