Background: diagnosis and treatment of thoracic actinomycosis is difficult. In most cases, surgery is performed to rule out lung cancer or to control severe symptoms such as hemoptysis. Methods: 6 patients with a mean age of 42 years underwent pulmonary resection and were given a pathologic diagnosis of thoracic actinomycosis at our institution between 2003 and 2010. We reviewed preoperative clinical characteristics, computed tomography findings, surgical indication, postoperative clinical course and outcome. Results: All patients were symptomatic. One patient had a history of cervical actinomycosis. The mean interval between radiographic identification of the abnormality and surgical intervention was 8 months (range, 4–17 months). Radiographic findings in all cases included a mass-like appearance, simulating lung malignancy or chronic suppuration. The various histological and bacteriological examinations had failed to make the diagnosis. Thoracic actinomycosis was confirmed after thoracic surgery. All patients received penicillin-based antibiotic treatment for at least 2 to 3 months. Good clinical results were observed in 5 patients. In one patient, we noted recurrence of actinomycosis after 10 months; it was a multidrug-resistant form. Conclusion: diagnosis of actinomycosis can be problematic because of difficulty in isolating actinomyces. In these cases, surgery is very helpful.