Hospital-acquired pneumonia remains a leading cause of nosocomial infections and is associated with significant rates of morbidity and mortality. Multiple host-, pathogen-, and intervention-related factors contribute to the development of pneumonia in this setting. Potentially deleterious impacts of illness or therapeutic modalities impair the host's ability to resist the development of pneumonia while in the hospital and predispose to a spectrum of pathogens of greater virulence than found in the community. Recognition of factors contributing to pneumonia in the hospital setting may offer the opportunity to intervene, minimizing, to the extent possible, the serious consequences of this nosocomial complication.