Simultaneous bilateral spontaneous pneumothorax (SBSP) during high-dose chemotherapy has been described in patients with pulmonary involvement by malignancy, including sarcoma, trophoblastic tumor, non-seminomatous testicular cancer, and non-Hodgkin lymphoma. We present a case of SBSP developing in a patient 11 days after a high-dose chemotherapy preparative regimen and stem cell transplantation without underlying pulmonary disease or evidence of lung lesions. It is important to recognize spontaneous pneumothorax as a potential complication of high-dose chemotherapy, especially in patients with known pulmonary lesions.