BACKGROUND: Actinomycotic infection is uncommon and primary actinomycosis of the lung and chest wall huts been less frequently reported. This disease may present as chronic debilitating illness with radiologic manifestation simulating lung tumor, pulmonary infiltrating lesion or chronic suppuration Diagnosis of choice was not definded yet and role of bronchoscopy on diagnosis was not described yet. METHODS: From 1989 to 1998, we experienced 17 cases of thoracic actinomycosis. We have reviewed the case notes of 17 patients with thoracic actinomycosis. The mean age at presentation was 53 +/- 13 years, 11 were male. RESULTS: Cough, hemoptysis, sputum production chest pain and weight loss were the commonest symptoms. The mean delay between presentation and diagnosis was 6.6 +/- 7.8 months. There were six patients who presented with a clinical picture of a suppurative lesion and eleven patients were suspected of having primary lung tumor initially. In no cases was made an accurate diagnosis at the time of hospital admission Associated diseases were emphysema (1 case), bronchiectasis (2 cases) and tuberculosis (2 cases). Bronchoscopic findings were mucosal swelling and stenosis (n=4), mucosal swelling, stenosis and necrotic covering (1=2), mass (n=3), mass and necrotic covering (n=1) and normal(n=6). Radiologic findings were mass lesion(n=8), pneumonitis(n=3), atelectasis(n=3), pleural effusion (n=2), and normal(n=3), Final diagnosis was based on percutaneous needle aspiration and biopsy (n=3), bronchoscopic biopsy specimens (n=9), mediastinoscopic biopsy (n=1) and histologic examination of resected tissue in the remaining patients(n=4) who received surgical excision Among 17 patients, 13 were treated medically and the other 4 received surgical intervention followed by antibiotic treatment Regarding the surgically treated patients suspected malignancy is the most common indication for operation. However, both medically and surgically treated patients achieved good clinical results. CONCLUSION: Thoracic actinomycosis is rare, but should still be considered in the differential diagnosis of a chrinic, localized pulmonary lesion Thoracic actinomycosis may co-exist with pulmonary tuberculosis or lung cancer. If the lesion is located in the central of the lung, the bronchoscopy is recommanded for the diagnosis.