Community-acquired pneumonia is a common medical illness, with clinical outcomes ranging from mild illness with rapid and complete recovery to a fulminant clinical course with morbid complications followed by death. A systematic review of the literature on pneumonia prognosis has identified a variety of demographic factors, symptoms and physical examination findings, comorbid illnesses, laboratory abnormalities, and etiologic agents that are independently associated with short-term mortality in patients with this illness. By combining these prognostic factors, investigators have developed a variety of indices to predict short-term mortality. Although these predictive instruments vary with respect to the patient populations studied, number of predictor variables included, statistical methods used, and overall clinical performance, these models can assist physicians in assessing patient prognosis and in making important management decisions such as the initial site of care (ie, home v hospital). Assessment of patient prognosis has also been used by clinicians and health services researchers who use the hospital severity of illness-adjusted mortality rate as a measure of the quality of medical care provided. Because the majority of patients with this illness survive, future assessments or predictions of prognosis in patients with community-acquired pneumonia should also evaluate a spectrum of other important health outcome measures including the occurrence of morbid complications, symptom resolution, quality of life, return to work and usual activities, and patient satisfaction with care.