We report a 67-year-old male with pneumonia in which Chlamydia pneumoniae was identified by serologic studies as the causative agent. After initial treatment failure with amoxicillin + clavulanic acid, pneumonia was successfully treated with the administration of oral azithromycin, 500 mg per day, for three days. Azithromycin is a new macrolide which has a long half-life and superior action to erythromycin. It provides a new and alternative choice in the treatment of Chlamydia pneumoniae infection in the future.