A 65-year-old man was referred to our hospital in July 2006 because of abnormality on his chest radiograph, and a CT scan revealed a 45-mm-diameter mass in the right S². Transbronchial biopsy failed to detect any malignant findings in July, and a significant reduction in the size of the nodule, to 30 mm, was seen in August. Therefore he underwent a CT-fluoroscopic lung biopsy, and the tumor was cytologically confirmed to be a non-small cell lung cancer. A right upper lobectomy was performed by video-assisted thoracosurgery in September, and the tumor was histologically confirmed to be a pleomorphic carcinoma. Spontaneous regression of lung cancer is extremely rare, and only a few documented cases have been reported, of which none was of lung pleomorphic carcinoma. Nevertheless, we concluded that we had encountered spontaneous regression of pleomorphic lung carcinoma.