Branhamella catarrhalis, formerly Neisseria catarrhalis, is a common bacteriological finding in the upper respiratory tract in infancy, and it ranks third on the list of bacterial causes of otitis media and sinusitis. In adults Branhamella catarrhalis may cause acute exacerbations of bronchitis and pneumonia, especially in patients with chronic lung disease. Branhamella catarrhalis is being recognized more frequently as a nosocomial pathogen and it may cause septicaemia in immunocompromised patients. Resistance to penicillin is prevalent and is due to production of beta-lactamases. The pathogenic potential of this agent should not be overlooked.