A 41-year-old man with productive cough was admitted to our hospital. His chest roentgenogram showed multiple small nodules in the bilateral lung fields. The nodules were revealed as intrapulmonary metastases of the adenocarcinoma of the lung. Systemic chemotherapy with paclitaxel and carboplatin was not effective, and continuous oral gefitinib therapy was initiated. Twenty-one days later, spontaneous pneumothorax was found in the left lung, and four days after that, in the right lung as well. The extent of the pneumothorax was slight; therefore, he recovered without drainage within several days. Spontaneous pneumothorax, especially bilateral pneumothorax, is a rare complication of chemotherapy for lung cancer.