Pneumonia is a life-threatening infection of immunocompromised patients, and accurate identification of the causative agent is essential for early initiation of appropriate antibiotic therapy. Percutaneous needle aspiration was used to identify Legionella pneumonia after sputum and bronchoscopy specimens had failed to provide a diagnosis in a 13-year-old leukemic patient with a lung abscess. We believe this is the first report of a child with this disease diagnosed in this way.