A 64-year-old woman underwent surgical resection of a posterior inferior pancreaticoduodenal arterial aneurysm in the subacute phase of acute aortic dissection (AAD). Concomitantly, a distal pancreatectomy was also required. The aneurysm was approximately 20 mm in diameter. Surgical resection of the aneurysm was performed because endovascular treatment was considered to be technically difficult due to dissecting lesions that had remained at the abdominal aorta. Histopathological findings suggested this aneurysm to be a pseudoaneurysm, which had arisen as a result of segmental arterial mediolysis. Approximately 1 year after surgery, no recurrence of the aneurysms was detected.