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Background: Influenza vaccination has been shown to reduce illness and all-cause mortality in vulnerable populations through the prevention of influenza infection. Attenuation of the severity of illness by vaccination has been reported for respiratory tract infections due to bacterial pathogens and would represent an important additional health benefit of influenza vaccination. We evaluated the impact of prior influenza vaccination on in-hospital mortality and other health outcomes among hospitalized adults with community-acquired pneumonia (CAP)., Methods: Consecutive individuals hospitalized with CAP during "influenza season" (November to April, 1999-2003) at hospitals operated by Tenet HealthCare were identified using a database constructed to improve quality of patient care. Associations between vaccination status and all-cause in-hospital mortality were evaluated using logistic regression models., Results: Among 17 393 adults hospitalized with CAP during the study period, 1590 (19% of those with recorded vaccine status) had a history of influenza vaccination in the current or most recent influenza season. Vaccine recipients were less likely to die in hospital of any cause than individuals without vaccination (odds ratio, 0.30; 95% confidence interval, 0.22-0.41). These effects remained significant after adjustment for the presence of comorbid illnesses and pneumococcal vaccination (adjusted odds ratio for death, 0.61; 95% confidence interval, 0.43-0.87) and under widely varying assumptions about individuals with missing vaccination status., Conclusions: Prior influenza vaccination was associated with improved survival in hospitalized patients with CAP during influenza season. This observation, if confirmed by other studies, would represent an important additional benefit of enhanced influenza vaccine coverage.