Pulmonary artery sarcomas are infrequently encountered and are often misdiagnosed before surgical exploration or autopsy. On clinical examination and conventional imaging studies, they are frequently mistaken for pulmonary emboli. To our knowledge, this case report is the first to describe the postoperative magnetic resonance imaging (MRI) appearance of residual disease of a pulmonary artery sarcoma and to assess the potential usefulness of MRI for monitoring such lesions postoperatively. Contrast-enhanced MRI, a relatively noninvasive method, seems well suited for postsurgical follow-up of pulmonary artery sarcomas.