OBJECTIVES: The study was aimed to 1) compare the costs of different antibiotic regimens in the treatment of patients diagnosed with pneumonia that required hospitalization, and (2) investigate if the initial choice of antibiotic affected the initial treatment success rates and death rates. METHODS: The study adopted a multi-center, retrospective case notes review design. Patients aged above 18 years old admitted to the Princess Margaret Hospital of Hong Kong during May 2005 to April 2006 and with a principal discharge diagnosis of pneumonia were included. Direct medical costs were estimated based on the medications, diagnostic tests, hospital stay and allied-health professional visits. The study was conducted from a public hospital's perspective. RESULTS: A total of 333 medical case notes were reviewed. The most commonly prescribed antibiotic regimen was amoxycillin-clavulanate (AC) regimen (63.7%) as compared to amoxycillian-clavulanate plus macrolide (ACM) regimen (17.4%), quinolone (Q) regimen (8.4%) and others (10.5%). The mean costs per patient for AC, ACM, and Q regimens were US $ 6992 (SEM: 353.4), US $ 6856.0 (SEM: 496.1) and US $ 6568.8 (SEM: 770.1) respectively. The treatment success rates for AC, ACM and Q were 66.0%, 77.6% and 78.6% respectively and the death rates were 13.7%, 0% and 14.3% respectively. The mean costs per patient for AC, ACM and Q regimens for patients with a history of chronic obstructive pulmonary disease (COPD) were US $ 8778.2 (SEM: 727.9), US $ 9762.7 (SEM: 1476.4) and US $ 6712.0 (SEM: 1216.9) respectively. CONCLUSION: There was no significant cost difference in the antibiotic regimens for pneumonia management. However, Q regimen was found to be superior to AC and ACM regimens in treating patients with COPD. Further studies involving more patients and study sites are needed to confirm the results.