A 60-year-old man who underwent treatment for diabetes mellitus showed elevated levels of serum carcinoembryonic antigen . Positron emission tomography-computed tomography (CT) revealed increased¹⁸F-fluoro-deoxyglucose uptake in a pulmonary nodular lesion in the right lower lobe and mediastinal lymph nodes. He was pathologically diagnosed as having primary lung adenocarcinoma (T2N3M0, clinical stage IIIB), and systemic chemotherapy consisting of carboplatin, paclitaxel, and bevacizumab was initiated. Eighteen days later, pneumothorax occurred in the right lung and drainage was done. After one course of chemotherapy, significant tumor shrinkage with cavity formation of the primary lesion was observed on a chest CT scan. Chemotherapy was then continued with no recurrence of pneumothorax. After four courses of chemotherapy, bevacizumab maintenance was continued for 15 months from the initiation of chemotherapy to primary tumor regrowth. Pneumothorax is a rare complication of chemotherapy for malignancy. We report a rare case of pneumothorax on chemotherapy with bevacizumab for primary lung adenocarcinoma.