A 65-year-old man who died of respiratory failure due to malignant hemangioendothelioma is reported. He was admitted to our hospital because of intractable hemoptysis. Chest roentgenogram revealed multiple patchy shadows in both lungs, but we could not make a diagnosis by usual clinical examinations including transbronchial lung biopsy. Since the patient's condition became critical, oxygen therapy, anticoagulants and antibiotics were started. In addition, corticosteroid therapy and double filtration plasmapheresis were performed since immunological disorder was suspected because of positive immunological examinations such as antinuclear antibodies and an increase in circulatory immune complexes. There was little response to the treatments and the patient finally died of respiratory failure. At autopsy, multiple tumor nodules were found throughout the lungs and the liver. Metastasis to mediastinal lymph nodes was also discovered. These findings made it impossible to confirm the primary lesion. Microscopy showed proliferation of anastomosing capillaries encasing tumor cells of unknown origin. Silver staining demonstrated capillaries encompassing the atypical cells, suggesting a vascular origin of the tumor. Furthermore, factor VIII related-antigen in the tumor cells was confirmed by the peroxidase-antiperoxidase (PAP) method. The final diagnosis of malignant hemangioendothelioma was made from these histological findings. Malignant hemangioendothelioma is rare, but is an important cause of intractable hemoptysis.