PURPOSE: Few available data exist to define either the medically necessary duration of parenteral antimicrobial therapy or length of stay for hospitalized patients with pneumonia. Therefore, we investigated the potential safety and effectiveness of a practice guideline recommending early conversion of low-risk patients with pneumonia from parenteral to oral antimicrobial therapy and early hospital discharge. PATIENTS AND METHODS: The practice guideline was studied retrospectively in 503 hospitalized patients with pneumonia at a teaching community hospital. RESULTS: Thirty-three percent of patients with pneumonia were classified as at low risk for complications and potentially suitable for early conversion to oral antimicrobial therapy according to the guideline. Were the guideline to have been used to guide patient discharge decisions, 619 additional bed-days would have been made available to accommodate incoming patients. A consensus among physician reviewers led to the judgment that quality of care would not have worsened for 98.2 percent of low-risk patients had they been switched to oral antimicrobial therapy on the third hospital day, nor would quality of care have been worsened for 93.4 percent of low-risk patients had they been discharged on the fourth hospital day. CONCLUSION: The practice guideline that we studied has the potential to safely reduce the duration of parenteral antimicrobial therapy and length of hospital stay for selected low-risk patients with pneumonia. The guideline should be studied in a prospective clinical trial.