Leiomyosarcomas are rare neoplasms of the smooth muscles. Primary pulmonary leiomyosarcomas, which constitute approximately 0.2%-0.5% of all primary lung malignancies, are extremely rare and highly lethal. They may originate from the smooth muscle cells of the bronchial wall, the blood vessels, or the pulmonary interstitium, and their rare occurrence, localization, and nonspecific clinical symptoms mean that correct diagnosis and proper management are often delayed. Here, we report a rapidly growing primary pulmonary leiomyosarcoma, which invaded the right atrium, vena cava superior, mediastinum, right hilar area, and left pulmonary artery within 4 months. On histopathology, a transthoracic needle biopsy of the mass confirmed leiomyosarcoma, and delayed presentation meant that there was a local spread to the neighboring structures at the time of diagnosis.