Three cases of pulmonary actinomycosis have been postoperatively diagnosed in our hospital in the past 3 years. All the cases were preoperatively difficult to differentiate from lung cancer, and all were diagnosed in men. One of the patients was diagnosed on the basis of clinical symptoms, while the other 2 patients were diagnosed during the treatment and follow-up of other diseases. On radiological examination, 2 patients showed mass-like shadows, and the 3rd showed a cavitary lesion; fluorodeoxyglucose (FDG) -positron emission tomography showed high FDG accumulation in all the patients. One of the patients was pathologically suspected with lung cancer on transbronchial lung biopsy. Right upper lobectomy was performed in 2 patients, and right lower lobectomy in 1. One of the patients who underwent right upper lobectomy, also received chest wall resection because of the perioperative finding of chest wall invasion of lung cancer. Clinically, all the cases were preoperatively diagnosed as lung cancer.