Invasive aspergillosis is a common form of fungal infection in patients with hematological malignancies. Because Aspergillus species have angioinvasive properties, they frequently disseminate from the lung to a variety of organs via hematogenous spread. Extra-pulmonary involvement occurs at an advanced stage of invasive aspergillosis, and represents an ominous sign. However, few reports have been published on extra-pulmonary involvement in cases of aspergillosis. Its clinical features have not been fully clarified. We experienced a patient who developed thyrotoxicosis and fatal airway obstruction caused by invasive aspergillosis of the thyroid. A 26-year-old man was admitted to our hospital for the treatment of non-Hodgkin's lymphoma. During myelosuppression following the chemotherapy, he developed cervical swelling and hyperthyroidism. We suspected lymphoma infiltration to the thyroid, and irradiated it with a total of 26 Gy. However, the cervical lesion enlarged rapidly, and he complained of wheezing and dyspnea. We underwent immediate tracheostomy to secure the airway, but he died. Autopsy findings were striking. Extensive necrosis with diffuse infiltration of Aspergillus hyphae was observed in the thyroid gland. Necrotic tissues of the thyroid protruded into the tracheal lumen, causing airway obstruction. This case demonstrated that invasive aspergillosis of the thyroid can lead to medical emergency.