Diagnostic imaging of the thorax is routinely used among both immunocompetent and immunosuppressed patients to detect infection, identify its complications, and aid in differentiating infectious from noninfectious intrathoracic disease. Imaging is more effective in suggesting specific types of infection in immunocompromised hosts where imaging findings can be combined with information on the patient's immune status, which in some cases allows treatment to be initiated without a pathologic diagnosis. CT imaging is particularly useful in immunosuppressed hosts with symptoms and minimally abnormal radiographs, such as those patients afflicted with bacterial airway infections.