In addition to the common respiratory pathogens, pneumonia can be caused by a number of unusual organisms, including chlamydiae, rickettsiae, fungi, and certain common bacterial zoonotic organisms. Because most of these pathogens are fastidious or have unusual growth requirements, the diagnosis often is made on the basis of serologic or histopathologic data. Unlike many common bacteria, the presence of any of these pathogens in sputum or other respiratory specimens almost always is indicative of significant disease. Because the clinical, laboratory, and radiographic abnormalities are usually nonspecific, it is important to obtain an accurate epidemiologic history in suspected cases of pneumonia due to these less common diseases. This article discusses some of the diagnostic and therapeutic aspects of pneumonia caused by some of these unusual organisms.