This investigation assessed the impact of initial empirical antimicrobial therapy on the outcome of therapy for community acquired pneumonia (CAP) patients and on patients' length of stay (LOS) in the hospital. Hospital records for 165 patients with pneumonia admitted to the Edward Hines, Jr. VA Hospital between 1 October 1997, and 31 March 2000, were reviewed. Criteria for CAP were met for 92 of 165 patients. Comparisons were made between patients treated with azithromycin and with other parenteral antibiotics (the reference group). No statistical differences were observed between the treatment groups for the risk factors. The azithromycin group patients were slightly older with a mean age of 69 years versus 66 years (P=0.23). Patients treated with parenteral azithromycin had on average, a shorter length of hospitalization namely 4.6 days compared with 9.7 days for patients treated with the other antibiotics (log-rank test, P=0.0001). In order to make the two groups of patients more alike we considered patients' data set without intensive care unit (ICU) admissions. The conclusion was the same namely azithromycin monotherapy was associated with a decreased duration of hospital stay.