An 8-month-old girl with respiratory distress and stridor was admitted to the authors' hospital. Two days later, she died of respiratory insufficiency due to pneumonia. Autopsy confirmed the presence of follicular bronchiolitis (FBB) in both lungs. After considering her clinical course, the authors focused on three pathogens: Legionella pneumophilia, Pneumocystis carinii, and Mycobacterium tuberculosis. Only Legionella pneumophilia was detected by both immunohistochemistry and PCR.