[A case report of pulmonary actinomycosis presenting as a mass shadow on chest X-ray].

A 58-year-old man admitted to hospital because of hemoptysis. Chest X-ray showed a large mass in the right middle lobe. A tumor marker CYFRA was slightly elevated. Despite a detailed examination after admission, no definite diagnosis was made. Lung cancer was suspected and a middle lobectomy was performed. Histopathological specimen of resected lung showed typical "sulfur granule" of actinomycosis. Pulmonary actinomycosis should be included in the differential diagnosis of a pulmonary mass lesion.