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Pulmonary actinomycosis frequently mimics lung malignancy on radiologic imaging studies. Positron emission tomography-computed tomography (PET-CT) is a useful diagnostic modality for differentiating lung malignancy from benign diseases. However, few studies evaluated PET-CT findings of pulmonary actinomycosis. Therefore, it is unclear whether PET-CT is helpful to distinguish lung malignancy from benign lung disease when pulmonary actinomycosis is clinically suspected. We investigated PET-CT findings in 11 patients with pathologically confirmed pulmonary actinomycosis. The median maximal standardized uptake value (SUV) on PET-CT of pulmonary actinomycosis was increased to 5.5 (interquartile range, 4.2–8.8), which was higher than the threshold value of 2.5 indicating malignancy. Pulmonary actinomycosis without central necrosis demonstrated higher maximal SUV of 7.5 (4.9–12.2) compared to 4.8 (3.2–5.6) of ones with central necrosis. PET-CT might be not helpful in differentiating lung malignancy from benign lesions when pulmonary actinomycosis is clinically suspected.