A very rare case of mycotic aneurysm in the descending thoracic aorta due to salmonellosis was treated in our hospital The patient was a 62 year-old male who 48 days before the operation was admitted to the depart,cent of internal medicine complaining of fever. nausla. vomiting, and loose stool. He was treated for 35 days and discharged. Three days after discharge, however, the patient was readmitted to the hospital comE긴ainin프 of $ulcorner$i포ht uppe$ulcorner$ 킥uadrant abdominal pain. Fever developed on the third hospiti린 day, and on the eighth hospital day, the patient complAined of back pain and epigastric pale. A simple chest x-ray showed evidence of hemothorax in the left plueral space, and therefore, computed tomography of the chest was done. The patient was diagnosed as a ruptured mycotic aneurysm of the descending thoracic aorta, and was transferred to our Department of Thoracic and CArdiovascular Surgery. The aneurysm and infected tissues was widely debrided, and the site was then patched with a Dacron graft. Salmonella choleraesuis was identified in the blood and aneurysm cultures, and antibiotics were administered for weeks according to the sensitivity of the organism. The patient experienced no complication thereafter and for the last three months since the operation, he has been leading a healthy and normal social life.