Pseudoaneurysm of the internal mammary artery can be a rare complication of surgery, particularly post-sternotomy, or determined by a direct trauma, usually a stab wound. This report presents a pseudoaneurysm by a stab, diagnosed by chest computed tomography scan performed for hemothorax recurrence. The patient underwent left thoracotomy in third intercostal space; mammary vessels were identified above and below the pseudoaneurysm sac and tied. The postoperative course was uneventful.