Spontaneous regression of a bulla in the lung is rare. We describe a case of spontaneous regression associated with the development of adenocarcinoma of the lung in a 59-year-old male smoker. The bulla had begun to regress spontaneously at least six months before lung cancer was detected on a chest radiograph. He underwent left upper lobe lobectomy with mediastinal node dissection. The tumor arose within the bulla, extending along the bulla wall. He has been alive for more than eight years with no evidence of recurrence. This case suggests that spontaneous regression of a bulla should be recognized as one of the early radiographic signs of the development of lung cancer in patients with bullous lung disease.