The authors sought to assess physician awareness and usage of American Thoracic Society guidelines for early conversion from intravenous to oral antibiotics ("switch therapy") in those with community-acquired pneumonia (CAP). We then determined if adoption of a CAP guideline would improve either. Patients (N = 510) hospitalized with CAP from June 2002 to May 2003 were identified retrospectively, and chart reviews were done on a random sample (130 [25%]) of these. Physicians were surveyed before and after guideline adoption. Community-acquired pneumonia guideline implementation increased physician awareness of American Thoracic Society recommendations (5% to 40%) and use of switch therapy (60% to 86%). Such use resulted in decreased overall length of stay from 3.6 to 2.4 days (P < .05) and from 2.91 to 2.41 days (P < .05) among early-switch candidates. Early-switch therapy was not optimally used prior to implementation of this CAP guideline. Adoption of the guideline increased awareness and reduced length of stay among inpatients with CAP.