PURPOSE: To investigate the value of the computed tomography (CT) in the study of diagnostic and post-treatment findings of pulmonary actinomycosis. MATERIALS AND METHODS: Clinical data and CT findings were retrospectively analyzed in 10 patients with histopathologically confirmed pulmonary actinomycosis. We analyzed the initial CT findings in search of patterns and distributions which suggest possible lung abnormalities and found the pleura, chest wall, and lymphadenopathy to be involved as part of the indicators of lung abnormalities. We analyzed follow-up CT findings for changes in the lungs after antibiotic therapy and recurrence after surgery. RESULTS: Of the 10 patients analyzed by CT for lung lesions, seven had been diagnosed with alcoholism and nine were male. The initial CTs (n=10) indicated that all the pulmonary lesions were solitary without chest wall involvement. However, a transfissural extension was observed in 20% of the study population (n=2). Furthermore, peripheral lung distribution and adjacent pleural thickening was observed in 70% of the study population (n=7). Within the consolidation (n=6) or mass (n=4), a central low density with peripheral enhancement was seen in 70% of the study population (n=7). A follow-up CT of the seven cases following antiobiotic therapy revealed that four cases showed minimal improvement or aggravation of their lung lesions, whereas three cases showed resolution or improvement. The improvement of the central low density was related to the improvement of consolidation or mass. Furthermore the presence of fibrosis was observed after the resolution of pulmonary lesions (n=2). No relationship was found between the duration and response of antibiotic therapy. A follow-up CT (n=4) subsequent to a lung resection revealed the onset of chest wall actinomycosis and a thickened pleura in one case. CONCLUSION: The results of this study highlight the value of the CT in pulmonary actinomycosis in order to diagnose and evaluate antibiotic responses, complications, or post-surgical recurrences of lung lesions.