Spontaneous pneumothorax is a rare manifestation of primary lung cancer and it is even more rare as an initial manifestation. Recently we have experienced three cases of lung cancer presenting initially as spontaneous pneumothorax. These three cases involved 2 men and one woman with an average age of 70 years [66 - 74years]. Lung cancer was discovered by explothoracotomy in two cases and by endoscopic biopsy in one case. In pathologic cell types, the one was alveolar cell carcinoma and the others were squamous cell carcinoma. We report these three cases of primary lung cancer presenting initially as spontaneous pneumothorax with review of the literatures.