The number of immunocompromised patients has increased over the past decades due to HIV infection, solid and stem cell transplantation, intensified chemotherapy and treatment of autoimmune disease. Pneumonia is a major cause of both morbidity and mortality in immunocompromised patients. Clinical management of pneumonia is difficult, since differential diagnosis in this setting is broad and includes both infectious and noninfectious processes. Because the development of pneumonia in immunocompromised patients is frequently life threatening, early therapeutic and diagnostic intervention is essential to obtain better outcomes.