Pulmonary tumor thrombotic microangiopathy (PTTM) is a fatal disease associated with malignant tumors that progresses to pulmonary hypertension. Gastric cancer is the most common cause, followed by breast cancer and lung cancer, whereas PTTM due to thyroid cancer has not been reported. In addition to pulmonary obstruction by tumor embolism, tumor cells stimulate endothelial cells to release angiogenetic factors, which induce remodeling of pulmonary arteries and veins and lead to lymphatic obstruction. There is limited information on the relationship between thrombus and PTTM. We herein report an autopsy case with PTTM which was caused by diffuse sclerosing variant of thyroid papillary adenocarcinoma, in which differential diagnosis included the acute phase of chronic thromboembolic pulmonary hypertension.