A male was diagnosed with squamous cell carcinoma on the right side of the tongue and underwent right hemiglossectomy and tongue reconstruction using a skin flap. Walking was initiated 16 days after the surgery, but he developed dyspnea and suddenly died 18 days after the surgery. Autopsy revealed a continuous thrombus from the right ventricle to the pulmonary arteries and fresh thrombi from the pulmonary trunk to the periphery in both lungs. His cause of death was considered to be pulmonary embolism resulting from movement of blood clots that formed after the surgery to the pulmonary arteries.