In this issue of Annals, Fee et al 1 present data suggesting tha the goal of antibiotics within 4 hours (PN-5b) for greater than or equal to 90% of emergency department (ED) patients admitted with pneumonia may not be attainable. The authors found that in 53 patients who received antibiotics after 4 hours (ie, PN-5b failures) and had a final presumptive diagnosis of pneumonia in the ED, 60% did not have radiographic evidence of a pulmonary infiltrate. These patients without a radiographic diagnosis of pneumonia represented 20% of the 153 patients eligible for PN-5b in their sample. According to performance standards, all should have received antibiotics within 4 hours of hospital arrival. Patients who received antibiotics after 4 hours were counted as quality failures by the Joint Commission for the Accreditation of Hospitals and Organizations (JCAHO) and the Centers for Medicare & Medicaid Services (CMS). This study shows that even in ideal circumstances in which patients are rapidly evaluated and treated, attaining 90% performance on PN-5b as recommended by the University Health Consortium may not be feasible. The authors concluded that JCAHO and CMS should consider changing the inclusion criteria for PN-5b to include only patients with clinical and radiographic findings that support the diagnosis of pneumonia, which would eliminate the troublesome criterion of “consideration of pneumonia” in the ED differential diagnosis. The ED differential diagnosis for patients with dyspnea or fever can often be quite broad, depending on when it is documented in the medical record. There have been 2 large retrospective studies demonstrating an association between antibiotic timing and severity-adjusted outcomes in pneumonia. 2,3 Issues have been raised about the validity of these studies, specifically with using associations in large retrospective data sets to make definitive conclusions or policies about quality of care. Although the 2 retrospective studies certainly suggest an association between antibiotic timing and mortality, neither was prospective, nor was either one a randomized trial. In these studies, attempts were made to adjust for other variables that may be associated with antibiotic timing and mortality, such as patient-level factors. However, as in all retrospective studies, the potential for unmeasured