From January 1997 to June 1999, we performed surgery in 17 patients with mycobacteria other than tuberculosis (MOTT), and 2 patients with lung cancer among them. Both patients had the diagnosis of MOTT by sputa bacterial cultures preoperatively, but no diagnosis of lung cancer. By computed tomography (CT) scanning, lung cancer was suspected in both patients, therefore they were performed video-assisted thoracoscopic resection of the lung. The diagnosis of malignancy was made by intraoperative frozen section of resected tissue, the patients were performed lobectomy with systematic mediiastinal lymph nodes dissection. According to increment of detection of the small peripheral lesion, infectious disease such as MOTT can be detected as small abnormal shadow by CT. However, it is difficult to distinguish malignancy from infectious disease preoperatively. Even if a preoperative diagnosis, of MOTT was made like present cases, diagnostic video-assisted thoracoscopic surgery must be performed, considering that lung cancer could combined with MOTT.