Abstract: The CT scans of 100 patients with lung cancer, interpreted as indeterminate mediastinal invasion, were retrospectively reviewed following thoracotomy. Forty-eight (48%) cases with lung masses were resectable without invasion of the mediastinum. Thirty-two (32%) focally invaded the mediastinum but were technically resectable, and the remaining 20 were unresectable because of severe mediastinal invasion. The CT features that were analyzed included the diameter of contact with the mediastinum, the fat plate, and the angles formed with the descending aorta and the mediastinum. We found that if the diameter of contact with the mediastinum was less than 3 cm or the fat plate between the tumor and the mediastinum did not disappear, it was almost certain that the tumor could be resected (>95%). The angles formed with the descending aorta and the mediastinum were insignificant for evaluation of resectability. Our results indicate that although CT is generally not helpful in differentiating lung masses with or without mediastinal invasion, it may play an important role in separating a large number of masses that are highly likely to be technically resectable.