Purpose: This study examines the strength of the association between vital-sign abnormalities, advanced age, and the diagnosis of community-acquired pneumonia (CAP) in the evaluation of adults with acute cough illness. Methods: A random sample of adult visits for acute cough to 15 EDs during the winter period of 2 consecutive years (2003-2005) was selected for medical record abstraction. Visits were initially sampled based on discharge diagnoses for a broad range of acute respiratory tract infection diagnoses. Participating sites were a national sample of EDs in Veterans Administration and non-Veterans Administration hospitals stratified across the US region. Results: Of 4464 charts reviewed, 421 had a diagnosis of CAP based on physician discharge diagnosis and radiographic findings. Age greater than 50 years and vital-sign abnormality (including fever, hypoxemia, tachycardia, or tachypnea) were the only significant predictors of CAP. Hypoxemia had the strongest association with CAP diagnosis (odds ratio, 3.5; 95% confidence interval, 2.4-5.0). A greater number of abnormalities were associated with a higher prevalence of CAP, from 12% with 1 abnormality to 69% with 4 vital-sign abnormalities (P < .001). Most vital-sign abnormalities were predictive of CAP regardless of age. Conclusions: Increases in vital-sign abnormalities are associated with a greater probability of CAP, and the strength of the association does not vary substantially by age.