Leiomyosarcomas of the pulmonary arteries are rare neoplasms seldom diagnosed during the patient's lifetime. We report a case of unexpected death in a 44-year-old man due to a leiomyosarcoma originating from the main pulmonary trunk and involving the right and left arteries as far as the lobar ramifications. The patient died after a 2-year history of bronchiectasis and chronic bronchopneumonia with weight loss and occasional episodes of syncope during the last 4 months. Immunohistochemical demonstration for alpha-smooth muscle actin was necessary to make a histological diagnosis of leiomyosarcoma. A review of pulmonary artery leiomyosarcomas is also presented.