BACKGROUND: The percentage of patients with community-acquired pneumonia (CAP) whose time to first antibiotic dose (TFAD) is less than 4 hours of presentation to the emergency department (ED) has been made a core quality measure, and public reporting has been instituted. We asked whether these time pressures might also have negative effects on the accuracy of diagnosis of pneumonia. METHODS: We performed a retrospective review of adult admissions for CAP for 2 periods: group 1, when the core quality measure was a TFAD of less than 8 hours; and group 2, when the TFAD was lowered to less than 4 hours. We examined the accuracy of diagnosis of CAP by ED physicians. RESULTS: A total of 548 patients diagnosed as having CAP were studied (255 in group 1 and 293 in group 2). At admission, group 2 patients were 39.0% less likely to meet predefined diagnostic criteria for CAP than were group 1 patients (odds ratio, 0.61; 95% confidence interval, 0.42-0.86) (P = .004). At discharge, there was agreement between the ED physician's diagnosis and the predefined criteria for CAP in 62.0% of group 1 and 53.9% of group 2 patients (P = .06) and between the ED physician's admitting diagnosis and that of the discharging physician in 74.5% of group 1 and 66.9% of group 2 patients (P = .05). The mean (SD) TFAD was similar in group 1 (167.0 [118.6] minutes) and group 2 (157.8 [96.3] minutes). CONCLUSION: Reduction in the required TFAD from 8 to 4 hours seems to reduce the accuracy by which ED physicians diagnose pneumonia, while failing to reduce the actual TFAD achieved for patients.