We present the case of a 41-year-old woman who presented with chest pain. CT for possible pulmonary embolism showed a mass filling the left main pulmonary artery, with imaging features suggestive of pulmonary angiosarcoma. Open thoracotomy for excision of the mass revelaed no mass, only evidence of a chronic pulmonary thrombus of the left pulmonary artery. We conclude that the radiologic features of chronic pulmonary thrombus may mimick those of pulmonary angiosarcoma.