Background: Actinomycosis is a rare infection caused by anaerobic or facultatively anaerobic, asporogenous, non-motile, Gram-positive, non acid-fast bacteria. The disease develops as a result of aspiration or inhalation of organisms from oropharynx, hemtogenous dissemination or extension
from adjacent-infected tissue.
Case report: 37 year old man was admitted to hospital with two months history of a fever, dry cough, chest pain and the large induration in the left part of the chest wall. Chest CT scan revealed the infiltration in the lingula with pleural thickening and effusion. Also, chest wall invasion without
rib destruction and enlargement of a lymph node next to vena cava superior were observed. Pleural biopsy revealed sulphur granules and the diagnosis of actinomycosis was established. Patient was treated by intravenous penicillin G (24 million units /day) for 6 weeks, after that period by oral ampicyllin 4g/d up to 6 months. Therapy was effective.
Conclusions: Awareness of actinomycosis is required in differential diagnosis of chronic inflammatory changes involving lungs and thoracic cavity. The suspicion of this disease is a key to proper techniques of collecting, and submitting specimens, and finally for diagnosis, and treatment.

Keywords: Actinomycosis, infiltration of the chest wall, Pleural Effusion, pleural needle biopsy