Branhamella catarrhalis is a Neisseriae-like organism that is the newest member of the family of pneumonic pathogens. The organism is seasonal, encountered only during the respiratory disease season. The majority of patients with pneumonia (80% to 90%) have underlying chronic pulmonary disease, and their clinical illness may be difficult to distinguish from exacerbations of lung disease by other causes. B catarrhalis is the most common bacterial pathogen in this setting after Haemophilus influenzae and Streptococcus pneumoniae. The organism is easy to identify in the laboratory, with a quality gram stain of sputum being the key to recognition. Most patients show patchy non-cavitary infiltrates on chest roentgenograms. Because 75% of isolates produce beta lactamase, empiric therapy with penicillin or amoxicillin is likely to fail. Recommended drugs include erythromycin, trimethoprim/sulfamethoxazole, amoxicillin/clavulanic acid (Augmentin), or one of the newer broad spectrum cephalosporins.