This study evaluated the possible changes in antibiotic use that might follow the implementation of British or North American guidelines for the treatment of community-acquired pneumonia (CAP) in The Netherlands. Patients admitted for mild, moderate and severe CAP were evaluated prospectively. Volume of antibiotic use, based upon guidelines of the British Thoracic Society (BTS), the Infectious Diseases Society of America (IDSA) or the American Thoracic Society (ATS), was estimated and compared to current practice. For 248 patients, current antibiotic use was 3087 defined daily doses. Antibiotic use would increase by 38% if based on ATS guidelines, by 23% if based on IDSA guidelines, and by 21% if based on BTS guidelines. The most significant increase in antibiotic use would occur for cases of moderate CAP, with incremental antibiotic costs of 1 750 000-3 500 000 Euros in The Netherlands.