Evidence based critical care medicine involves integrating clinical experience, expertise, and patient preferences with explicit, systematic, and judicious use of current best evidence in making medical decisions. Published evidence has many sources: research from the basic sciences of medicine, and from patient-centered clinical research on the accuracy of diagnostic tests, the power of prognostic markers, and the effectiveness and safety of preventive, therapeutic, rehabilitative, and palliative interventions. When critically appraising a clinical article for potential use in intensive care unit (ICU) practice, the first question we ask ourselves is: Is this study valid? If examination of the study methods reveals that the design is rigorous, we can turn to the two other key questions: What are the results? and, Will the results help me care for my patients? This approach may aid in the interpretation of an article on therapy or prevention; in it we discuss a strategy designed to prevent ventilator associated pneumonia in critically ill patients.