Bacterial and fungal contaminants have been identified in marijuana samples and thus are a potential risk factor in the immunocompromised patient using it as an antiemetic. We describe the development of an invasive pulmonary aspergillosis in a patient using illicitly obtained marijuana as an antiemetic during combination antitumor therapy for small cell lung cancer. Although this patient had multiple risk factors implicated in the development of invasive pulmonary aspergillosis, the infectious potential of inhaled marijuana must be recognized. Further study of this potential health risk in needed.