OBJECTIVES: The primary objective of this analysis was to identify factors associated with prolonged length of stay (LOS) in patients with hospitalized community acquired pneumonia (CAP). METHODS: Data were collected retrospectively on 1861 randomly selected patients with a discharge ICD-9 diagnosis of CAP who were admitted between October 2000 and April 2003 to 29 hospitals in the Great Lakes region. A standardized electronic database was used to collect demographic and clinical data. Logistic regression analysis was used to adjust for potential confounding variables and to identify patient factors associated with a LOS greater than 4 days (cohort median). Pneumonia Severity Index Score (PSI) defined risk class. Antibiotic selection was evaluated relative to standard guidelines (Infectious Diseases Society of America). RESULTS: Patient factors associated with a LOS greater than 4 days included admission during the 2001-2002 season (OR, 1.35; 95% CI, 1.06-1.72), increasing age (OR, 1.01; 95% CI, 1.00-1.02), Risk Class III (OR, 1.50; 95% CI, 1.10-2.06), Risk Class IV (OR, 1.67; 95% CI, 1.20-2.32), Risk Class V (OR, 3.01; 95% CI, 2.0-4.76), ICU admission for pneumonia (OR, 2.11; 95% CI, 1.31-3.40), gram-negative sputum culture (OR, 2.15; 95% CI, 1.37-3.38), gram-positive blood culture (OR, 2.01; 95% CI, 1.28-3.17), increasing hours to antibiotic administration (OR, 1.02; 95% CI, 1.01-1.04), modification of empiric antibiotic regimen (OR, 1.45; 95% CI, 1.17-1.81) and intravenous to oral antibiotic conversion (OR, 2.01; 95% CI, 1.63-2.48). Administration of antibiotic regimens consistent with IDSA guidelines was associated with reduced odds for a longer LOS (OR, 0.50; 95% CI, 0.33-0.77). CONCLUSIONS: Several factors were associated with a hospital LOS greater than 4 days. Guideline-compliant antibiotic use was associated with reduced odds for a long LOS. These findings may facilitate further research and the development of targeted management strategies to control LOS and ultimately resource consumption.