Mucormycosis is a rare, opportunistic infection caused by fungi of the order Mucorales, class Zygomycetes. These fungi produce fatal opportunistic infections in immunocompromised patients, especially in those with severe neutropenia. Recently, mucormycosis has become more widespread, because potent, myelosuppressive chemotherapies are performed more often than before. Nevertheless, this infection rarely occurs in patients with solid malignancies. Here, we describe an autopsy case of disseminated mucormycosis in a neutropenic patient who was receiving chemotherapy for an underlying solid malignancy. A 31-year-old Japanese man received cytotoxic chemotherapy with etoposide for the pulmonary metastasis of a secondary malignant fibrous histiocytoma. This patient had long been treated with chemotherapeutic agents for this solid cancer and for the preceding eosinophilic granuloma, both of which were highly resistant to the therapy. During the treatment with etoposide, his neutrophil count declined to less than 100/μl. He presented with high fever and severe dyspnea. Pneumonia was highly suspected. The chemotherapy was discontinued, and granulocyte colony-stimulating factor was administered. Although the neutrophil count recovered, the pneumonia progressed. The patient experienced respiratory failure and died 17 days after the onset of this episode. An autopsy revealed dissemination of mucormycosis not only in the lungs but also in the liver, the spleen, the kidney, and in the digestive tract. The therapy-related severe neutropenia, and the probable impairment of the immune system, because of the previous chemotherapies, would have been responsible for this fatal infection.