Some patients present in the outpatient setting with persistent respiratory and constitutional symptoms in association with unresolving parenchymal infiltrates on the chest radiograph. Clinicians must entertain a wide differential diagnosis as many infectious and noninfectious conditions can lead to this chronic pneumonia syndrome. The clinical presentation and radiographic abnormalities are often nonspecific. A significant proportion of patients have no underlying predisposing illness, and most of the bacterial pathogens are often considered constituents of the "normal respiratory flora." Accurate diagnosis generally requires bronchoscopic evaluation. Prolonged therapy is essential. This article reviews the epidemiology and the predominant bacterial, mycobacterial, and fungal pathogens associated with this syndrome. A brief discussion of some of the noninfectious processes is also included.