STUDY OBJECTIVE: To determine if early mobilization (EM) of hospitalized adults with community-acquired pneumonia (CAP) reduces hospital length of stay. DESIGN: Group randomized trial. SETTING: Three Midwestern hospitals. PARTICIPANTS: Four hundred fifty-eight patients with CAP admitted to 17 general medical units between November 1997 and April 1998. INTERVENTION: EM was defined as sitting out of bed or ambulating for at least 20 min during the first 24 h of hospitalization. Progressive mobilization occurred each subsequent day during hospitalization. Measurements and results: Intervention (n = 227) and usual-care patients (n = 231) were similar in age, gender, disease severity, door-to-drug delivery time, and IV-to-po switchover time. Hospital length of stay for EM vs usual care was significantly less (mean, 5.8 vs 6.9 days; adjusted absolute difference, 1.1 days; 95% confidence interval, 0.0 to 2.2 days). There were no differences in adverse events or other secondary outcomes between treatment groups. CONCLUSIONS: Like patients hospitalized with acute myocardial infarction and total knee replacements, EM of hospitalized patients with CAP reduces overall hospital length of stay and institutional resources without increasing the risk of adverse outcomes.