Although aneurysms of the thoracic aorta are easily recognized on computed tomography (CT), nonaortic intrathoracic aneurysms and pseudoaneurysms are unusual and not often encountered by radiologists. These lesions can result in complications such as hemorrhage or symptoms from mass effect. In some cases, patients may be asymptomatic and the aneurysms may represent incidental findings. Radiologists should be familiar with the CT appearances of these rare vascular abnormalities to enable prompt diagnosis. The goals of this pictorial essay are to: (1) illustrate and describe the CT appearances of various unusual intrathoracic nonaortic aneurysms and pseudoaneurysms; (2) discuss the etiology and clinical significance of these lesions; and (3) discuss management options where appropriate.