Rationale: Previous use of inhaled corticosteroids (ICS) in patients with chronic obstructive pulmonary disease has been associated with increased risk of community-acquired pneumonia. However, ICS have been associated with fewer pneumonia complications and decreased risk of pneumonia-related mortality. Objectives: The objective of the study was to assess the influence of previous use of ICS on the incidence of parapneumonic effusion in patients with different baseline respiratory disorders. Methods: We conducted a single-center cohort study of 3,612 consecutively collected patients diagnosed with community-acquired pneumonia. We assessed clinical, radiographic, and pleural-fluid chemistry and microbiologic variables. Patients were classified according to whether or not they received prior ICS treatment. Measurements and Main Results: A total of 633 patients (17%) were treated with corticosteroids before the diagnosis of pneumonia (chronic obstructive pulmonary disease, 54%; asthma, 13%). Incidence of parapneumonic effusion was lower in patients with ICS use compared with non-ICS patients (5% vs. 12%; P < 0.001). After matching according to propensity scores (n = 640), prior treatment with corticosteroids was still significantly associated with a lower incidence of parapneumonic effusion (odds ratio, 0.40; 95% confidence interval, 0.23-0.69; P = 0.001) compared with patients without ICS treatment. Prior ICS treatment was associated with higher levels of glucose (P = 0.003) and pH (P = 0.02), and lower levels of protein (P = 0.01) and lactic acid dehydrogenase (P = 0.007) in the pleural fluid. Conclusions: Prior treatment with ICS in a population of patients with different respiratory chronic disorders who develop pneumonia is associated with lower incidence of parapneumonic effusion. Copyright © 2013 by the American Thoracic Society.