We would like to report a rare case of post-stenotic aneurysm of the pulmonary trunk and its left branch in a 51-year-old man. His cardiac disease, which was first diagnosed at the age of 4, was left untreated because of absence of symptoms and normal physical development. A CT scan, recently performed because of decrease in exercise tolerance and worsening dyspnea, showed a pulmonary artery aneurysm (52 mm x 79 mm). The echocardiography revealed a severe pulmonary commissural stenosis. Through a surgical approach the pulmonary trunk and its left branch were excised and reconstructed using a 30 mm Dacron graft; the right pulmonary branch was then reimplanted on the right side of the tube. The patient's postoperative course was uneventful. He was discharged on the seventh postoperative day and there were no adverse events or complications at 1- and 3-month follow-up.